Which only works if you keep an ear out for new cars being released, or actually have the time to play it.
I've got every single one so far, but thats because i don't have much of a social life.
But yeah. They're probably 1,000,000+ so that the manufacturers get a bit of commission every time a GT player buys one. Sadly, i suspect one day this will actually be true (maybe not with GT, but still).