Second only to Hex Wrenches, Toy Cars are hard to find, and can only be located in dressing tables. That said, there are two single locations that they can be obtained, and also offers the chance of a Gold Necklace and Antibiotics at the same time. As always, if you don't get what you want, relog to reset the loot.

Head to District Union Arena (Hyena Stronghold), move to the street G PL NW and you'll see an alley. Head to the bottom of the alley and next to a green truck is a dressing table. 

Alternatively, head to the Theater settlement, exit through the main door (where they move the vehicles) and take the left entrance. Once outside, head immediately right into the first building and follow the corridor until it leads you outside. There's another Dressing Table there waiting to be looted.