The Yahoo Groups have a Files and Photos section with a lot of good information.
Keyport Car and Foundry has some Civil War train parts (trucks, link & pin couplers) but he is only online via email but you can question him on the Civil War groups.
Your best bet is to do the Civil war in 1/72 scale. Bachmann has cars that are available in sets that are aproxamately 1/76th scale, model trains OO scale. The Bachmann oldtime 4-4-0’s are HO scale and are too small for the cars.
IHC made Oldtime 4-4-0’s that are excellent models for OO scale Civil war era. They also made a cattle car that is an excellent Pennsy model. The Model Power/Mantua Old Time freight cars, too tall for HO, are perfect for OO scale Civil War models
An IHC 4-4-0 with a 1/76 scale figure
There are many sets of soldiers for the Civil War in the 1/76/1/72 range.