I would check Hemmings, I am pretty darn sure that the early 70's Corvettes used the same 4 Piston Caliper.
When SSBC first started out they rebuilt Corvettes and AMC 4 piston calipers. I would think if the bore and stroke was close enough or exact you could use them. They are probably dead on. It would probably be easiest to find. Then again I could be wrong but for some reason...