There is a 1/24 Bentley Blower originally released by Heller and re-packaged by Union in Japan, and other companies as well, quite frequently found at e-bay, not very expensive.
On the other hand I have never seen Napiers etc. from this vintage, I think if they exist they do it as limited-run resins. 
There is an 1/24 Alfa Romeo Mille-Miglia by Heller, and a few pre-war French street cars (Delages, Delahayes, Bugattis, Renaults) by Heller now out of production but often seen at swap meets and e-bay.