I've seen them parked next to the Lifeinvader offices and in the streets nearby, I've seen them by Weazel and the nearby intersection, I've seen them driving on the twisty roads with the houses in the hills and parked in some of the driveways there. I also occasionally see them in the lot ON Del Perro pier (not the lot next to the pier on the beach, but the parking ON the pier itself.) I've also seen them at times in other areas, but those are the primaries. Seen them at times next to Eclipse, as well. I think it also may depend on what you're driving to some degree with some of these, as well - if you're driving a similar style of car you may have better luck.
Additionally, the best way to find a car in this game is to not be actively looking for it. It will then somehow appear.