On my games it is in the box or on the sleeve the cd came in. If you have lost it or your does not have one I would say the only other way to get it is to contact the maker of the game by e-mail and ask their techs. Hopefully they have a way to bypass the key code for your disc(a way to find the code without having to pay anything). I have found some sites that say you can use a search program to find your key code/serial number but they also say they have yet to find one that actually works.(so I would be kind of leery/leary of using them).