http://search.msn.de/results.aspx?FORM=REIN&q=%C3%B6ffentliche%20Transportmittel%201945
Best place to start. Try not to expect much though, alot of searches for World War details past weaponry, and such is not often documented.
I think in the 1940s, most of the vehicles were created by Mercedes. If I recall my history correctly, Mercedes did not merge with Benz until after the war. Your search is probably best spent trying to find out the manufacturers then moving on to specific makes.
Have found in the past this was the best case trying to research Russian vehicles of The Cold War.