All DLC's are downloadable through update patches of the game, you'll have all the DLC cars, tracks and features once all the patches are installed. Most of them are Vision cars.
The DLC you want is probably the pre-order exclusive 15th Anniversary car pack, you could only get it through pre-order back then, so now you have to persuade someone around who hasn't used the pack yet, considering your copy is the same region as your PSN account.
