Aeroclub Models has the 1/72nd M-2 in white metal. You can find it here:
http://www.aeroclub-models.com/p.html?n=14&c=G015
I've ordered several items from them and the biggest problem is that they are relatively inexpensive and you have to buy several items to get to their minimum cc order of £5. Not much of a problem at all, I stocked up on M-60's and GPMG's. The rest of their 1/72 weapons are here:
http://www.aeroclub-models.com/s.html?c=15&cn=AEROCLUB+1%2F72+GUNS
The Cobra Company mini-guns are for the M-134 system, so you'll have to make a mount for them. But they do look good and come with rocket pods that you might also be able to use.