I do wonder that aswell. They say the development has stopped. Maybe they were just talking about improving gameplay and such like. But they may still add spotlight cars as it doesn't really require much development.
I can only assume you have to complete an expert race in a obsure car to win this And they will never be found in the AC. I haven't been able to win any of these. Although I will try again for this. I know I know. Get good. Yet life goes on.