I would check the Classic Toy Trains section of these forums, since they would know better than those of us here. Off the top of my head I'd say Google for Lionel parts dealers (there are tons of them, though the ones I see at train shows seem to have only vintage parts), and check eBay for the part, or a donor loco.
If you're running DC, you could wire the motor in the loco could be reversed with the direction switch on the powerpack. AC would require at least a mechanical reverse unit.
Nelson
Ex-Southern 385 Being Hoisted
I have a lionel steam engine, that has a reversing circuit board . The board is bad, engine will only go one way. Lionel is out of the board, does anyone know where I can purchase a replacement? Also is it possible to run without the board installed?