The Gosvamins frequently cite various Samhitas, Tantras and Agamas in the course of their presentation.

Some of the samhitas and tantras mentioned in Sat Sandarbha:

Maha-samhita,
Narayana-samhita,
Katyayana-samhita,
Jabali-samhita,
Agastya-samhita,
Garuda-samhita,
Sanat-kumara-samhita,
Vaisnava-tantra,
Mrityu-sanjaya-tantra,
Brihad Gautamiya-tantra,
Sammohana-tantra,
Trailokya-sammohana-tantra,
Svayambhuvagama,
Unspecified Agama-sastra.

Additionally, in Hari Bhakti Vilasa, we find the following among others:

Parasara-samhita,
Vaisvanara-samhita,
Jaimini-samhita,
Yajnavalkya-samhita,
Narada-tantra,
Devi-agama,
Siva-agama,
Unspecified Agama.

The paddhati of Dhyanacandra Gosvamin cites the following sources for the various mantras for arcana he presents.

Gaura-mantra -- Urddhvamnaya-samhita,
Nityananda-mantra -- Brahmanda Purana,
Advaita-mantra -- Padma Purana,
Guru-gayatri -- Padma Purana,
Guru-mantra -- Brihad Brahmanda Purana,
Gopala-mantra -- Gautamiya-tantra,
Kama-gayatri -- Svayambhuvagama,
Radha-mantra -- Gauri-tantra,
Lalita-mantra -- Sammohana-tantra,
Visakha-mantra -- Brihad Gautamiya-tantra,
Citra-mantra -- Skanda Purana,
Indulekha-mantra -- Isana-samhita,
Campakalata-mantra -- Garuda Purana,
Rangadevi-mantra -- Kisori-tantra,
Tungavidya-mantra -- Kisori-tantra,
Sudevi-mantra -- Rudra-yamala,
Asta-manjari -- Kisori-tantra.

Does anyone have further information on the origin of the texts cited? I am more or less aware of the history of the various Puranas, but of the Samhita, Tantra and Agama I have no clue.

Needless to say, some of these texts just don't exist and never have.

The Haribhaktivilasa is probably the most reliable in terms of genuine sources, but even there, many of the works haven't been found.

The original Pancharatra texts mostly come from South India in the first millennium. The earliest date to the 5th or 6th century. However, suprisingly, few of these books have been used in the HBV or any other Gaudiya work. One would expect some evidence of these Agamas in HBV, but there is little.

There seems to have been a strong Pancharatric tradition that was useful to the Gaudiya outlook--(Brihad) Gautamiya Tantra, Narada-pancharatra, Sammohana-tantra, Mrityu-sanjaya-tantra, Tantra-bhagavata, Krishna-yamala, to name a few of the main ones. We have textual problems with nearly all these works, where there are extant versions available. Almost none of these works attained any kind of canonical status in Gaudiya Vaishnavism and thus there is no tradition of preserving them.

Ultimately, no matter what Siddhanta Saraswati said about Pancharatric influences dominating Bhagavata influences in the Gaudiya tradition, it appears that the ritual/mantra/magic mindset of the Pancharatra always played a subsidiary role, with the Bhagavata activities (sravana-kirtana-smarana) (or rasasvadana) predominating.

Siddha-pranali alone doth not a Pancharatra make.

Anyway, we are hoping to get to the bottom of this eventually. The GGM will provide very useful tools for solving some of these problems. We have known that Narada Pancharatra was a problem, but the discovery that one entire book is just a copy of the Krama-dipika was an important one. If we could ever able to discover the copy that Rupa and Gopala Bhatta were using, that would be very helpful.

You confirm my doubts about the sources of Dhyanacandra's paddhati. What about the claim that Brahma Samhita was written by Mahaprabhu Himself? It is tailor made for Gaudiya Siddhanta. Is the text mentioned by any other sampradaya?

I don't think he restricted this to mean only Dhyanacandra's paddhati.

Should we doubt the sources of Gopal Bhatta Gosvami and Sanatana Gosvami in Haribhakti Vilasa?

nana shastra vicaranaika nipunau sad dharma samsthapakau - vande rupa sanatanau raghu yugau sri jiva gopalakau.

And the Sandarbhas.

I am not advocating that anyone doubt or not doubt. It's just that the legitimacy of many sources cited is very hard to prove. I opened this topic to explore the extent of information available on the various books cited.

In some cases, just judging by the types of text quoted, I cannot believe that they did not have a genuine manuscript available to them, which is currently available. This would include such things as Narada-pancharatra, the current text of which does not include much of what the Goswamis found in their edition.

On the other hand, some enthusiastic authors like Dhyana Chandra took advantage of the fluid nature of certain texts to ascribe materials to them that did not exist. My feeling of this is a slight sadness--why did he feel it was necessary? Would it really have hurt the cause if he openly admitted that either he or an associate was the composer of these mantras? But that is my viewpoint. There were many who felt and there are many who still feel that some kind of scriptural imprimatur is necessary to support any innovation.

For all we know, Kisori-tantra may have been composed by the sadhu next door from Gambhira who kept one copy for himself and handed the other one to Dhyanacandra to check it out.

After all, Dhyanacandra didn't make any claims on the origin of the texts, did he? He just cited them.

Here is something that I found in a simple google search about siva agama

http://www.sivaagama.com/english/eagamas.html


also found this at http://www.veda.harekrsna.cz/encyclopedia/scriptures.htm

An interesting note on Maha-samhita:

It is documented there as a text cited by Madhva. If this is the same Sanatkumara Samhita cited in various Gaudiya texts, that becomes interesting.

Madhva seems to quote from Narayana-samhita as well in his commentary on Mundaka.

This gives an idea about their dating, at least pre-Madhva texts.

A bit more googling.

Agastya-samhita:

Some Sri Vaishnavas say that the year of Ramanuja's birth is mentioned in this samhita.

Garuda-samhita is suggested as one of the samhitas of the Buddhist era (ca. 600 B.C. - ...):

Mr. Brzezinzki has been looking for Mrityu-sanjaya-tantra and Sammohana-tantra without much success:

I wonder if he's had any success. Sammohana-tantra, in addition to Gaudiya sources, seems to be frequently cited in sakta-circles.

Svayambhuva Agama is a Saiva-agama, one of the 28 main texts. (Orientalia)

I couldn't find anything on Katyayana-samhita or Jabali-samhita. There is a Jabali Upanishad though, a Saiva-text. I take it that Vaisnava-tantra is a generic reference.

That more or less covers the sources of the Sandarbhas. Any further bits of information on these texts? A good majority among them do not advocate Vaishnava-siddhanta, that much is evident.

Here is from private letter by russian follower of kaula-tantra (he obviously cites some text in English, but doesn't name it):

Well, when I think of the number of sadhus, who could compose and composed different shastras... I beleive, that all of them existed, but few of them became so prominent like Brahma Samhita to survive during the centuries...

If we exclude the texts cited in the Sandarbhas and in Hari-bhakti-vilasa, including Garuda, Brahmanda and Padma Puranas, we are left with the following ambiguous sources for Dhyanacandra:

Gaura-mantra -- Urddhvamnaya-samhita,
Radha-mantra -- Gauri-tantra,
Indulekha-mantra -- Isana-samhita,
Rangadevi-mantra -- Kisori-tantra,
Tungavidya-mantra -- Kisori-tantra,
Sudevi-mantra -- Rudra-yamala,
Asta-manjari -- Kisori-tantra.

Ekkehard Lorenz on Urdhvamnaya:

Urdhvamnaya-tantra is the text with Kripa-kataksa-stava. A verse on Mahaprabhu is sometimes cited from the text. Urdhvamnaya-tantra certainly sounds like a text where one might find a Gaura-mantra. At least Bhaktivinod does in the pramana-khanda of his Navadvipa Mahatmya (1.46). I don't know of any earlier references. Perhaps the Tantra and the Samhita have swapped places in the text of Dhyanacandra.

Gauri-tantra -- Cited in DhPad 163 and 181 on Radha-mantra. Google is silent.

Isana-samhita -- Mentioned in Nepal News: "According to the Isana Samhita, Lord Shiva manifested himself in the form of a huge Jyotirlinga, to determine who is the greatest divinity among trinity (Shiva, Vishnu and Brahma)." Rather obscure!

Rudra-yamala -- Cited in DhPad 292 for Sudevi-mantra, a rather well-known Saiva-agama.

Kisori-tantra -- Cited in DhPad for two sakhis and asta-manjaris. No information anywhere.

That really leaves us only with Gauri-tantra and Kisori-tantra for Dhyanacandra to account for.

Of course it is another matter whether the verses cited are found in any current editions; whether it be the verses in Dhyanacandra's text or in the various other Gaudiya works.

Excuse me for jumping in here, but what about the possibility that the goswamis could access the Vedic texts through mystic congnition much in the same way that Sanjaya was able to invision the battle of Kurukshetra within his mind while setting in the palace of Dhrtarastra? After all, isn't mystical cognition the way in which Vyasadeva accessed the Vedas and divided them into four parts?
Maybe Mahaprabhu acquired the Brahma-samhita by the same manner?
Is the Gaudiya ontology bereft of any mystical element? Does everything always have to answer to the practical and the mundane?

Even I had a dream just the other night of seeing a very special book. It was bound in the most elegant and attractive manner. I have never seen a book that looked so beautiful and special.

I don't remember being able to read anything in the book, but it was shown to me and I could understand that the book was very sacred and contained special writings. I also saw a holy man dressed in white with his hands folded in pranam.
There were some other very spiritual-like dreams I had that night.
Sometimes I have bhava-like dreams where I am weeping in ecstacy.

The trouble with scholarship is that it tends to ignore the mystical aspect of life and seek to validate everyting within the realm of the external senses. However, there is a very mystical element in the Bhakti culture and indeed the chanting of the maha-mantra is a mystical meditation. Pure devotees attain all the mystic siddhis, though they never use them for personal ambitions. Somtimes the mystic siddhis can be employed in devotional service.
This might be some sort of explanation of how the master-yogins like the six-goswamis could access Vedic knowledge from the akashic plane. There is a billion verses of the Puranas on the heavenly planets. Vyasa reduced them down to an essential 400,000 verses. However, through the power of mystical cognition he could access a billion verses of the Puranas alone.

Scholars will never validate the mystical aspect if knowledge. For them everything has to be answered in terms of mundane historical records and accounts. This is ultimately a very lame approach to the supra-mundane aspect of spirituality. Actually, everything about spirituality is supra-mudane. There is very little mundanity in transcendence. It is beyond the realm of scholarship. Transcendence is the realm of the yogis, not the scholars. Therefore, Lord Krishna says in the Bhagavad-gita:
tasmad yogi bhavarjuna (6.46)
O Arjuna, in all circumstances, be a yogi.