Questions about Origin/CD Keys

So I picked up a copy of 'Simcity' for $2 at a thrift store. Atlas human anatomy frank netter. It says Copyright 2013 so I assume that's 'SC2013'? I read the back of the box and it said it needed the origin client, account, etc, and a CD Key. I figured since it was a thrift store find it wouldn't work. Got everything going and of course, the key was already used. I searched google for a place to buy a cd key for it, but all the sites are either for European version of the game, or seem kind of sketchy. Is there a place I can buy an activation key for this game directly from a trusted source?

I haven't played Sim City in years since I had an old Windows machine, some 15 years ago, and would like to get back into it! I hope there's a way to get a legitimate key for this game. If not, are there older versions that are legally/easily obtainable? Even SC2000 would make me happy!