Again, have you ever heard of retail? Guess not...
Let me help you: http://www.g2play.net/store/Diablo-3...-Download.html
Another CD-key for Diablo 3, also legal: http://www.freerecordshop.nl/games/d...-5030917102578
Tadaa, legal key bought as if you were in a store. How hard is that to understand?