Thank you Chris Goodwin for the excellent information and the suggestion I may have some useful information.
Chris Goodwin mentioned the main sources of Car Wars counters available. Car Wars counters were also created for The AADA Vehicle Guide Volume 2 and The AADA Vehicle Guide Volume 3.
The two Car Wars Adventure Packs, Midville and Muskogee Mayhem, each had Car Wars counter sheets.
Car Wars Expansion #10: Deluxe Wheelie contained multiple sheets of Car Wars counters from previously-published Car Wars products.
Cardboard Heroes Set 18: Car Warriors did not contain GURPS Autoduel vehicle counters, but it did have a nice selection of GURPS Autoduel pedestrian counters.
The Web page below has hyperlinks to a large number of Car Wars counters that could be enlarged for GURPS Autoduel.
Zen Car Wars Paper Counters Page
http://zenseeker.net/PaperMiniatures/CarWars.htm
I have seen top-down photographs of Hot Wheels, Matchbox, and other 1/64 die-cast cars on the Internet to be used as Car Wars counters. These images, which I cannot find at the moment, might be able to be enlarged for GURPS Autoduel.