Legally, the only thing you can do is buy the game again-luckily it is less than $15 now a days, so it is a cheap replacement...just let this be a hard lesson learned to take care of your disc better in the future-as if you had kept them in the case the game comes in when not in use, you would not have lost them...
If you are prone to losing game discs easily, you can get the download version off Steam(has the game for less than $5 the last I checked-there was even a topic on here that said that recently) OR D2D/Amazon/gamestop...this way there are no discs to worry about...
That's the only legal options you have i'm afraid...
Grand Theft Auto IV
