My dad had a number of them from years ago, but lost track of them. The black ones.
I do have two very rough castings though. Both are sand castings made using the "rubber" model as an original pattern, and cast in what I am sure is scrap aircraft magnesium or aluminum.
They were bought from a craftsman in Italy, late 1944. If I had a LOT of time and energy, I'd clean them up. For now, they are interesting but rough.
Frog made them out of plastic ( I think) in England during WW2.
I did find references where modeling clubs did do group build efforts. Rings true to me.
I found one source that claims Collectaire made a series of wood models for that purpose, for hobbyists to assemble.
The Cruver Company in Chicago made a majority of the ones for the US, according to two sources I found. They were cast in cellulose acetate, which was a non-essential material. Their usual products were things like fountain pen barrels, buttons, eyeglass framews and such so I suppose it was a straightforward thing.