Where to find 7 1/4 rear end shock plates??

Have you checked doctor diff? I think the 8 1/4 and 7 1/4 share the same plates
No. 8 1/4 takes 3" U bolts, 7 1/4 takes 2 1/2" U bolts. I don't know of any place that repros 7 1/4 plates.
OP, if all you did was snap the shock studs off, just put new ones on your old shock plates. Mancini has 'em.
Mancini Racing Lower Rear Shock Stud