I'm curious exactly which screws for Graflex people are having trouble obtaining. As far as I know, none use unusual threads, and I haven't found any that I cannot replace by cutting down some existing screw.
Everything is American thread, UNC and UNF, with a couple of minor exceptions. There are some short wood screws that are unusual, and there are several shoulder screws and the like that were either made by Graflex or made for them. I work on Series B, D, Speeds and Crowns pretty often.