As far as I can tell, there's only 3 safety car models in the game:
-Nissan Skyline R34 pace car;
-BMW M3 safety car;
-SLS AMG safety car.
(I might have screwed their names, I can't remember them)
The R34 you can only get by getting gold on all license tests, the other two comes up on the mileage exchange quite frequently, you just need about 5k miles to buy them.