Well, currently Dixie Gunworks, and EAA, both a manufacturer and importer. And since you mentioned some defunct companies I guess we are turning on the wayback machine and I'm not sure how many that will add. Allen F.A. and KBI come to mind. There was a Replica Arms Co. or something like that, not sure if they are still around. Might have been related to Navy Arms.
BTW, I don't think Buffalo Arms is an importer, as far as SAA's go. They primarily sell Cimarrons.