Mantua locomotives are among my favorites. These locos were first produced in the 1940’s and 50’s and are tough and reliable. Here are a couple resources for locos and parts.

Loco kits – http://www.jaystrains.com/HO-HOn3/Locomotives/hosteam.htm

Parts and remotoring – http://yardbirdtrains.com/index.htm

Remotoring – http://www.ablehobby.com/Alliance%20repower%20Parts.htm