San Juan Car Company, whilst specialising in narrow gauge (0n3, 0n30) offers a range of parts and ready to run cars for the 0 scale enthusiast.
From 0 Scale News :
Manufacturer. O Scale power trucks & detail parts, primarily for electric cars, and scratchbuilder supplies. O Scale standard and narrow gauge freight car, locomotives, and detail accessories; narrow & standard gauge freight car kits, RTR cars, trucks, track hardware and details.
San Juan Car Company Western Pacific 40ft box car kit