I've seen some very old forum discussions re: whether a C4 frame would fit on a C3. Concensus seems to be "no", that it would be expensive to alter and make it work.  Others mentioned a good C3 frame could be available for 1/2 the price...so I've joined this forum to inquire if anyone out there has info on where to possibly find a frame for a 1970 Stingray Convertible.  Appreciate any input! 😊

There is a Corvette salvage yard in Bristol, Pennsylvania called Contemporary Corvettes.  You might give them a call.  800-367-8388

Thank you. Are all C3 frames universal, i.e.will a '68 fit a '70?

I suspect there are minor changes from '68 to '82. For instance, I believe the roadster had some additional bracing.  While a non-matching frame might be able to be modified, It might require some serious welding.

I'd look for a 69-72.  The 68 was a bit of an odd ball and the 73 on have energy bumpers so I don't know if they are interchangeable without modifications.