you don’t need a fully functional car (as everyone say they are rare, but some exist)
Certain cars are very easy to fix:
find a car that’s in nearly ok condition (with a broken seat/controls/battery/tires, or just lacking fuel/battery charge) replace it with a makeshift welder + wrench, or just fuel up, and you got yourself a car.
I usually fix up military vehicles/ RV’s/Road Rollers/Electric cars that i find in acceptable condition and take 'em to my base.
Now, if you want to do vehicle with mechanics < 2, or with no welder… whatever anyone else said:
Garages, home garages, bridges sometimes spawn working cars, while some solar cars may work out of the box too, or can be very easily fixed with a jack + tires.