The only models that *really* have interchangable stocks are the higher-end MP5's such as the Tokyo Marui, Classic Army, and the new VFC model.
ICS is a bit of a off-beat brand. The stocks most likely will not fit on the CYMA MP5, without MAJOR modification. So, either buy the model you want, or forever be in denial.
Oh yeah, save your money. Buy a MP5 worth owning.

By the way: Don't start a new topic- Use your existing one. Chances are, people will read it. This forum is for gas guns, GBBR's, and GAS SMGs. Use the AEG section in the future.