@Rowan maybe you should start another search. Instead of Volkswagen Käfer, try KdF Wagen. Here the story of the KdF Wagen. Hitler planned the KdF Wagen as a means of getteing every German family his own automobile. KdF reads Kraft durch Freude (loosely translated Strength through Happyness.) The program demand the ordinary German to save 990 Reichsmark, 5 Mark a week, which was a lot of money for the ordinary worker. I theory, when he saved the money, then he could pick up the car at the Fallersleben plant. Until the start of the war, 630 KdF Wagen were build build, but their were delivered to Wehrmacht units. Wehrmacht means all forces of Germany including Luftwaffe. It is proofed that Luftwaffen had KdF Wagen but the Propaganda rather photographed Me109 and Stukas than ordinary cars.
After the war, the KdF plant was renamed Volkswagen Werk and the settlement build around it was named Wolfburg. The term VW Käfer came up in the 1950´s when in Germany the Wirtschafts-wunder (Economy Miracle) started.
HTH
No one ever received a car through that stamp program, unfortunately.
Hermann is correct; Käfer is a post-war term.
Cheers for the new feedback everyone 
Regarding my online searches, I don’t think I ever used the word “Käfer” - it’s a while ago, but I think I was going by the term “VW Type 82” (or something along those lines).
I’ve kept the basically finished kit in mothballs at the decals stage in case evidence of a Luftwaffe licence plate turns up, but I’ll probably end up going with the earlier suggestion of using it as a visiting army vehicle to add a sense of scale to an aircraft model in a vignette. I’m just about to build an Fw 190F-8, so it could be a believable scenario to have an army liaison officer helping plan an urgent ground attack mission.
All the best
Rowan