I'm grafting a 1990 GSX-R750 front end onto my race bike. It came with only a single disc and caliper, which is probably plenty for me. I may want to do some testing with the second set installed, however, so I need to find a second caliper. Mine is a Nissin four piston which I assume is stock. Finding either an identical one or a complete replacement pair would work for me. The question is, how generic are the calipers? Are there other model years or other bikes I can get them off of and bolt them directly onto mine?

If im correct the 88-92 750 all use the same rotors and calipers.

the calipers from the 88-92 750's are all the same, but the rotor design changed in 90 (slotted instead of cross-drilled).

Thanks for the replies. Is it likely that calipers from a later model would work? For example on eBay there are frequently calipers for unspecified model year GSXR's and I'm wondering if I can make them work.

All the calipers for the 310 mm rotor will work as they fork lowers use the same spacing, including the 6 piston versions thru '95. The 6 piston ones are your best bet.
I put those on my 91 with a ZX7 master cylinder (1mm bigger piston) and it was a huge improvement.