There is a very big chance that the last car you will need to obtain this achievement is 2 door Packard Custom (13th on the list). There is very easy way to obtain it.
First of all you need to ignore the solution saying you can get this car in The Gas Man case. The car simply won't spawn. I've read that they replacet the car with InstaHeat car.
All you need to do is play the Street Case Hot Property. Drive after fleeing suspect but DON'T TRY TO STOP HIM and ignore Packard Customs ( If you are aiming for 100% completion you need this car saved in your gallery). The one you MUST get is behind the truck the suspect will crash at the end of the chase.