Sorry if I came across as harsh. Unfortunately, we get a few people who come in here expecting help with pirating games. You wouldn't believe some of the stories they come up with to try to pretend to be legit. As a result, I tend to be a bit sceptical - especially if the poster is new.
Whilst sympathetic to your plight, I can't imagine many people willing to give up their CD key, and thus not being able to play the game online. It is, after all, one of the finest multiplayer games ever made.
Your best bet is to try online stores - who tend to stock a wider range of games than high-street shops - or even ebay (although beware pirated copies there).
Is there no way to recover your CD key some other way? Through Battlenet perhaps? I can't imagine you're the first person to lose the CD...