Jerry is right. Within the past several decades what remaining NG equipment is still with us, especially restored equipment, has found its way to the hands of museums, tourist RRs, and a few private owners.
However, deals do happen. Watching this board could turn up leads. For example, the Alder Gulch operation in Montana disposed of some unrestored passenger cars and other equipment last year. Restored equipment for sale is very, very rare; why sell after such an investment? But you never know when an estate sale could happen. As a group the restoration-minded seem to be getting older - fast!
Bob of AZ