I found a Bravado Buffalo, Sports (online) in the north (middle of the map) parked at Up-n-Atom just west of store (7/20), Mt Chiliad area. Actually, a sweet red one pulled up also as I was taking this picture. I'm going to the Mod Shop now.
Not sure if this is the car you're looking for though.
Edit: You can only mod it slightly in looks. Minor skirt and spoiler changes.