There were reunions of Qunatrills raiders up untill 1917 or so. Per Edward Leslies book "the devil knows how to ride the story of WCQ and his conf raiders Frank James was quoted at such a meeting in 1913 saying (not his exact quote) that both sides did a fair amount of evil but read the book its very good. I don't know if you could contact the author but it would be interesting if you could. Quantrills group was by no means the only group of bushwackers so they may of had reunions but I dont know if they kept transcripts. Approx 40k Mo men enlisted in the various conventional Conf regiments which are listed in civilwarregiment.org. I would imagine that they did have reunions. Keep in mind that in those days it wasn't has easy to keep records of what was said has it is today. It would of been possible for someones daughter or grandaughter who was a secretary to use shorthand and then type the miniutes at home I don't know if they did that. Don Johnson who is on this forum might know if such transcripts survived. The state of Mo and various counties have historical societies it would be interesting if they could locate transcripts.
Let me know if you turn up anything,
Leonard