Shoei made one some time ago. REALLY rare, and expensive if you happen to find one. Its an external gas version, that used the BV system.
If you want an easier obtainable version, than your only real option would to be to mod it from another
gun. The G3 is the most likely candidate. Its actually bade really closely off the real one in real life, and the whole body and barrel are pretty much identical. Take a picture of a g3 and compare it to an mp44, and youll; see what im talking about.
I was actually thinking of doing this a while ago, but I just didnt have the money, and it would take alot of sheet metal working to make the grooves and magazine and barrel shroud and such.
Im more concetrated on fininshing my .30 browning right now.