Good luck. The first step IMO, however is to find out who organized the conference. They usually retain a copy of most presentations. Try finding the agenda as an alternative. There, you have the names of the speakers and their corresponding organizations. Only after identifying these (sure) participants, researchgate makes sense, I think.
@HistoPol I did try the Congress website. I may be failing at internet wrangling, but I couldn't find a way of contacting them. However, researchgate.net is new to me - thanks, I'll give that a try!
I'm also about to thank and confuse the College of Heralds, who were very helpful with questions about William Marshall, by sending them a photo of the finished piece!