Not all of the cars in GTA IV are found on Free Mode. Here is a list of the cars WILL spawn during unmodded Xbox 360, PS3, and PC Free Modes (NOTE: This is only for the original GTA IV, not TLAD or TBOGT). New cars spawn every game hour in a specific order. Any gang variant of a car that spawns online will be in the game (i.e. the Cavalcade has a gang variant. The Cavalcade spawns online, meaning it's variant will too.)