The excellent Syriacologist Steven Ring has discovered that a good catalogue of all the Syriac manuscripts at Harvard is online here. Better yet, he’s going out there to take a look at them.
Among them I notice as Ms. 95 a copy of Nestorius, The Bazaar of Heracleides, on which I have written before. Colophons in this suggest that it is not a direct copy of the only manuscript, the now lost Kotchanes manuscript, but via an intermediary.
In Ms. 106 are extracts from the letters of Ignatius of Antioch. Perhaps some might be from other letters than the 3 known to and published by Wm. Cureton?