I think that, if you wanted to do this, you'd probably need to do it in two steps:
1) get 50 custom CD-Rs printed (these would be regular blank CD-Rs with a custom label of your design).
2) burn whatever music you want onto those CD-Rs yourself using iTunes or similar.
I doubt you'd be able to find a company willing to create the final product for you, as that would basically make them (and you) commercial music pirates ;D. One exception, though, would be something like mixandburn.com, but each custom CD there would cost around US$10-$15 depending on the number of songs you want on it. Your decision, adventurer.