For starters, the game files are called ROMs. They are illegal, so we can't post links here (and you can't ask for someone to email you a link either). I'd suggest searching on Google for "<name of game> rom". For example, "Super mario 64 rom". Most N64 ROMs will be of file types like .v64, .z64, etc., so you could probabl also search for them with "super mario 64 v64"