It's hard to explain when I haven't seen the movie, but here goes.
I bought a 6AA or 8AAA pack of Duracell Batteries I believe and included was one of the Cars. Similiar like when they package the mini flashlights. I've only seen three of them and got the main character of the movie. I didn't open the package, if I have time I can post a pic later. They are all pullbacks I believe and have a quick release mechanism. It can be a Street Pump or a Cone.
I got it from an autoparts store. They also has bigger not Duracell versions that all do something special. The tow-tuck can Tow, the other has lights, etc.