1. Make sure you are level 24, and mine was 4,816,000ish
2. Go to the B license tests, pick B2. After it loads, advance to B3, and keep doing that all the way to B6. Exit, go back to the Used car lot and check for it. You should have 30 new cars in there.
3. If its not there, repeat step 2. I got it in about an hour doing this, but who knows how long it will take you, hopefully not too long.
Good luck!