Honestly, my recommendation, if you're really that preliminary, is to not do this as a conference paper. Even if you limit this to "historical societies discussing feudalism in the second half of the 19th century in England" it still sounds like it has the scope of an MA thesis, with all of the attendant research time (probably a lot more than a few hours). The whole thing sounds like a book.

But, this idea does sound fascinating in general. I'd start by looking at very early editions of Speculum and the other journals and looking at the footnotes and watching out for any references to societies.

This actually hits really close to my dissertation topic, which focuses on scholarly circles of antiquaries from the mid 16th century to the end of the 17th. I'll try to point you towards some resources, mostly centered around London, from this period.

First up would be the Elizabethan Society of Antiquaries around the turn of the 17th century, members included William Camden, John Stow, William Lambarde, and Robert Cotton. There is a collection of their papers and minutes printed by Thomas Hearne in the 18th century called A Collection of Curious Discourses. They met fairly regularly in Cotton's library until they were encouraged to disband by James I. I doubt that would be considered the oldest such society, as there were more informal groups surrounding John Bale and John Leland in the 1530s, Matthew Parker's household, William Cecil's "salon," and the patrons of John Dee's library in Elizabeth's time. But it would be difficult to call them organized societies (with the possible exception of the scholars working in Matthew Parker's household--but they were perhaps more interested in Ecclesiastical History and Protestant polemic than general historiography).

You might also try digging through some letter collections. John Selden's correspondence is available online here and here. His letters are a great window into the scholarly networks of the mid 1600s. Look also for both Henry Spelman and his son John. These three were kind of a network hub for scholars interested in history and antiquities and they had connections everywhere. Later in the century (and into the next), the letters of Humfrey Wanley, George Hickes, and Thomas Hearne might prove useful.

It may be obvious, but the Philosophical Transactions of the Royal Society would be a great place to go. In its early days, there was a strange overlap between antiquarian, archaeological, and numismatic interests with the natural philosophy of the early scientists. The Royal Society of Antiquaries didn't split off until the 18th century, and even then there were some who maintained memberships in both societies.

I haven't spent a lot of time with them, as they are a bit out of my timeline, but you can find some really interesting historical debates taking place within 18th century publications like the Gentleman's Magazine.

For some secondary sources, some good ones would be Graham Perry's The Trophies of Time, Rosemary Sweet's Antiquaries, Anthony Grafton's Worlds Made by Words among others, May McKisack's Medieval History in the Tudor Age, a number of works by Joseph Levine (mostly 18th century), and Jennifer Summit's fantastic Memory's Library.

Sorry if this isn't exactly what you're looking for as a lot of this was actually published, but I do hope that some of it proves fruitful. Good luck!

Two recommendations that might help:

• Bonnie Effros, Uncovering the Germanic Past (2012). Effros looks at the development of Merovingian (early medieval France) archaeology. She's more interested in how specific concerns pop up (e.g. ethnicity, sexuality, religion, etc.), and 19c. France is by no means 19c. Britain. But it might give some insight on how to research the correspondence circles that shaped medieval historiography outside the academy.

• Garth Fowden, Before and After Muhammad (2014). The first few chapters could make an excellent stand-alone essay on the early development of medieval and late-antique historiography, i.e. Gibbon et al. Fowden works as an art historian, which shapes how he narrates the rise of medieval studies, and he's especially concerned with how academics came to divorce Islamic and medieval history into two separate fields. His narrative is good for reference, and his footnotes might be worth close study.

I'd keep correspondence societies in mind. I'd also think about antiquarians, particularly those who engaged in archaeological excavations such as Sir Thomas Browne (not to be confused with the later antiquarian Bishop Browne), and also collectors like Sir Robert Bruce Cotton. Especially prior to the 19c., remember that there's no hard divisions between history and other disciplines, and that there was little attention to keeping the middle ages separate from other periods, since neither the 'middle ages' nor the historical discipline had yet been adequately formulated. My impression is that most people working on early historiography avoid these thorny issues by focusing on individual biographies.

I'd recommend finding a couple names that sound like people you're interested in, then doing a Proquest dissertation search for them. It's always one of my first stops to help me develop research bibliographies. Good luck!