For AR parts, we know PK Firearms will be there and Model 1, J&T, and I think M&A are usually there. You can find plenty about them on here. The "gun shops" there--Plainfield Shooting Supply, Midwest? (green tables from Fort Wayne), Albro's--I've dealt with and had no problems. Lots of smaller tables that I've not paid a lot of attention to. Watch your pricing though. It's not uncommon to see the same thing on two tables with a huge price difference, or to see things for more than you could get them for at your local store.
Sunset Weapons in Danville has been at all of the shows I've gone to. I don't know if they'll be at this show or not, but there's been some talk of them having some troubles lately and people having issues with them. As I recally they mostly had Class III stuff on the tables, so you probably wouldn't buy from them anyway.