Well, I can give some information about ISSS and Super Copa in Argentina and Uruguay. While Super Copa is pretty uncommon to find it CIB (it seems there weren't many copies back in the SNES days), ISSS, on the other hand, is one of those uber classics that happen to pop up here and there all the time. Not cheap of course. ISSS is considered the ultimate SNES' sports game and everyone wants it. I'm afraid to say they are goddamn right. That game is glorious not just for soccer fans, but for anyone that understands soccer rules and dynamics (or Captain Tsubasa's fans, as myself).
Apart from that, Super Copa is not a good soccer game. Bah, which soccer game could be good after playing ISSS? I guess that made a big part on Super Copa's rareness: nobody gave a damn about it, as they were too busy playing ISSS until the sequel came out on PSX and N64.
I have Spanish Super Copa's box anyway (as well as ISSS CIB), and I'd gladly take some pictures if you want.