Nippon Sharyo was prime contractor for the most recent deliveries of METRA cabs and cars. A major subcontract for carbody fabrication was let to Super Steel, Milwaukee.
http://rides.webshots.com/photo/1342446 ... 2115cjdMnv
As Mr. Railnut notes, Colorado Railcar builds specialty cars that are fabricated with carbon steel. That is one thing for an operator such as the land cruiselines (and their Love Tub "parents") that are prepared to devote "TLC" to their fleet - something different for a public transit agency that never has or will have enough funding to properly maintain their fleet (Mr. Railnut, is your Metro North really any better in that area than Amtrak - was that potty I was sitting adjacent to on 1451-12OCT- ever so "pungent").
Somehow, I think doubt could be raised if any builder that has maybe built 100 "specialty" cars since its inception could even be considered a responsible bidder for an order of 200 cars (that is what I think Amtrak would be looking for to reequip the Regionals) to be fabricated from stainless steel.
But two things of which I'm certain; there will be an order placed during this decade for new Corridor cars, and that the foreign prime contractor will have substantial work, especially final assembly (better photo op for pols with cars rolling off an assembly line than being unglamourously off loaded from a ship), done here in the US.