Does anyone know if Heinzelman & Sons is still in business or offering to cyanide color firearms? With all the hazards of cyanide and the advent of more modern heat treating processes I can't imagine many shops still mess with real cyanide salt color case hardening.

Not double guns but at about the 2:20 mark the Uberti SAA clone salt bath hardening process is shown - https://m.youtube.com/watch?v=qYOJa8ZNxmE