It's a DIY project at present if you want one, nobody makes one. That said a couple of the available 28mm ranges M9s look much closer in shape and size to the M20 than the original so worth looking. IIRC Crusader or Artizan's version fall into this category.
I did ask Kosta about doing one for the Portguese and the 1960s Brits. No idea if that's on his very long to do list.
Note to manufacturers. Korea was an interesting conflict and more than just WW1 trench warfare with WW2 weapons. It would be worth a decent range. Late Korean War era US Army troops would be extremely useful, for later conflicts, as various third world proxies and ideal for playing 1950s pulp Godzilla, it came from outer space type games