We obtained some cab side number plates in South Africa. There the railroad would make them available to the railway museum in Johannesburg once an engine was scrapped. I seem to remember back in the 70's the price for a sold brass cab side number plate was about $8.00 U.S. I recently sold one to another railfan that was brought back here on a freighter in 1976. I am keeping one and sold the other. There were two plates per engine, one for each side. In 1984 when I made my last trip, there were no cab side plates available. But we were able to purchase GMAM(Garratt), tender plates. These are much smaller but similar looking oval plates. I bought 2 for about $8.00 each.
Still had soot on them, as the security guy found out when he unwrapped them from the newspaper the museum had wrapped them in. He was not happy!!! I am not really a collector of RR artifacts but those two GMAM plates are near the fireplace on display. They mean more to me than most folks who see them. Anyway some things can be obtained without stealing. In the old days steam was being scrapped at two locations west of Cincinnati. They got engines from the L&N, N&W, NYC, B&O, and maybe others shipped in. I know a couple guys who told me they bought stuff from those scrappers, like number plates, bells, headlights, gauges, whistles, and builders plates.
Greg