You’d need to dump your own copy of GT5 from a PS3 disc and use RPCS3 (open-source emulator). Torrenting it remains piracy and against this sub’s guidelines.
2. THE EXCLUSIVE 3. THE DOWNLOAD
: You must dump your own legal copy of the Gran Turismo 5 disc to an ISO or folder format. Note that "Spec 2.0" is the most complete version of the game.