Which cars, exactly?
Vacca, some others. I heard they actually appears on streets after patch. I got Vacca for Kifflom quest but it never respawned for me in the same place. I don't understand why you can't find them on streets. I NEVER saw Cheetah outside of that mission.
Not that driveway, there's a different one in Rockford Hills that the Vacca spawns at 100% of the time. Check YouTube.
And the Cheetah is only available from the internet. It doesn't drive around on the streets.