First- - - - - -look for a counter man at the parts store who has at least half a head of gray hair. Ask him if he can read a printed catalog. If nobody in the store meets that description, RUN, do not walk, out the door! Today's wet-behind-the-ears computer terminal operators couldn't find an elephant in a shoebox, much less a part that doesn't jump off the computer screen at them!
Unless you live in a town with both city limit signs on the same post, there's probably a local electrical parts rebuilder somewhere nearby. Someone who can take a pile of parts and build an alternator, or (Gasp!) a generator, can get you set up with exactly what you need, the right way, the first time!
Jerry