I think a new club would work as long as there were limits to production years. For instance, Nash through 1956, Hudson through 1957, Kaiser Frazer through 1955, Packard through 1956, Studebaker through 1964(?)
I understand some manufacturing concerns went on after these years and owners with those cars could join the club and participate BUT I think - for instance - AMC implies later years participation.
Also, for instance, the Oldsmobile crowd is strongly divided between the younger OCA which caters to muscle cars and the AOCA (or whatever the older crowd's club is) which only goes into the early 60's if I recall.
So, I think it is time to do this. Many orphan clubs are proud to be "orphan" owners. It would make for better club driving tours, more solvency, more magazine content and better attended meets.