Here are a few that come to mind off the top of my head. This list is by no means complete; these are just the ones that spring to mind immediately.
Larry's Truck & Electric (A.K.A. LTE Rail, A.K.A. LTEX)... located in Ohio, I believe?
National Railway Equipment (NRE)
RELCO (located in Iowa)
CEECO (located in Washington state)
VMV-Paducahbilt (Kentucky) (They're owned by somebody else now... I want to say NRE...?)
Beacon Locomotive Services (located in Texas)
Ozark Mountain Railcar (located in Missouri)
Western Rail (located in Washington state)
And dozens of others that I can't think of at the moment... not to mention the hundreds of railroads that would surely have a few turbos in their spare parts warehouses.
Also try the classified ads on www.RailSwap.org