Not sure if anyone was looking or not, but here is part numbers for the Gen 2 gas valve sub assy and piston.
Gas Valve Sub Assy - 1810577-R
Piston - 1810015-R
I will state that the extra Gas Valve I purchased is adjusted different then the one that came with my MPX, the new one is not flush it has about 2 threads sticking out, so I'm not certain it will perform the same as I have not had time to test. I plan on doing some testing once I get a chance to hit the range and also once I get my Form 4 approved from June 6 of last year.