Hi Rubicon, I have just got a third Opel Blitz to convert into a flak wagon. I was hoping to use a 37mm Flak 36 or flak 43.
The 20mm flak in all variants is available from a number of sources, but, unfortunately no seems to do a 37mm flak in 1/56 scale.
This might be a good place to start.
Cheers
Tim