1. Go to the parking lot of the prison.
2. Go to Online > Options, set spawn to "Last Location" instead of "My Apartment"
3. Keep joining new sessions till one appears in the parking lot.
I can 100% assure you it will eventually spawn. Once you find one, drive it to the nearest mod shop to insure it and put a tracker on it, it can be kind of tough to get it all the way back to your garage.
"Just look at the flowers Lizzie. Just look at the flowers."