Steal it or get a friend to give it to you. Or stop being one of the idiotic members of the unwashed masses who mindlessly follows every game with a gun on console with drool pooling and be a real gamer. BO2 is no different from any other CoD 'cept the guns are moderately useful in adaptive playstyles. Ditch the lost cause that is CoD. Get a PC.
You can pirate it. There are various ways to do it such as usenet newsgroups or bit torrent sites. However, that's about as much info as I can give you without violating the rules. If you look around, you'll find a way. Just keep in mind that software piracy is illegal.