Jealous. Been looking out for one of these in GTAO for an age.
You can find it on the mission "No hey bronca" that you request from Gerald. You have to be in it at the end when you or someone else kills the gang leader. When you get to free rome, you will be sitting in it. After you buy a tracker and insurance, it won't go in your garage the first time. Just start a new session and it works fine after that.