While on vacation, my wife & I visited Rocky Mountain Train Supply in western suburban Denver recently. While they're primarily an N-scale retailer they have also been buying & reselling used trains of all scales. So I was happy to find an MTH O Premier TOFC car in Great Northern paint at a very fair price. They also had some used O engines ranging from $40 -- $1200, plus a complete line of Woodland Scenics buildings and other stuff that OGR people would typically use. Friendly & helpful staff people, nice crowd on a Saturday morning and they discount for cash buyers. The only caveat is that their website will not feature the used stuff, that will be on a "show up & see what they have" basis.
Rich in SD