Ok, need some more help. The guy I am buying this from said "this gun comes from the factory on a National Match Frame,these guns are normally built on Brazilian made frames and when they run out of parts at the factory they use Natinal match Frames until more Brazil frames are aquired,I have sold probably 40 of these guns in the last year,and about 8 have been built on these frames. This gun actually has a NM prefix serial number".
Don't have any knowledge of your question on the frame, I have seen stranger things so would not doubt it, but have not ever heard of anything to confirm it either.
As far as price goes my local dealer here in TX has a Mil-Spec model #PB9108 (I think that is the one you are refering to) listed in today's paper on sale New $399.84. That's the best I have seen lately.
As part of Springfield's shooting sports sponsorship program, we had four Mil-Specs as prize table guns, and they had the NM frames. A local gunsmith looked them over, and he thought that the slides and frame were actually matched; I don't remember his reasoning, and I never actually saw the guns, but this guy was convinced that they were not mil-run mil-specs. All Springfield frames are "made" in Brazil.
NM serialed pistols are finished in the US. N serialed pistols are finished in Brazil. My regular Mil-spec is a NM frame. It's a good shooter out of the box, and a tackdriver after i replaced the bushing.
The National Match frame is an internet rumor. This was beat to death on the springfield forum, until Springfield themselves clarified the matter on the forum. The price is good though, buy the pistol. You'll like it.