I had this exact same problem yesterday, where I just wanted to get a Beetle Cup Car from the Amateur German Touring Car championship.
I had already won the Lupo cup car and the Opel Astra touring car, so I was quite annoyed when for about 15 times in a row it would award me another Lupo or the Astra. Eventually it gave me the 3400S (which I also already owned), then another Lupo, then finally, the Beetle Cup Car. So just keep on trying.
I do believe the prize car awarded is fully randomized, but one thing I tried just before getting the 3400S was to let the race go a little bit, then exit. Before I was exiting almost immediately, surely less than a second had passed in each race.
If you've ever programmed with random numbers you'd know about seeding the random number pool. I guessed that they were seeding with the time, and with all my races ending with the same time (or in a pattern that is fixed, either 0 or 1 full seconds), it's possible that the random number generator would continually give me only two values. This is purely speculation though. IDNWFVC: I do not work for Visual Concepts.
