Light socket replacements

I am helping my son redo some of the wiring for the lights on the rear of his truck (1994 Ram 2500). We need to replace several of the light sockets which have apparently been chemically exposed (it was a farm truck). I am have looked but have been unable to locate an internet source for oem light sockets. Even the few dealers that I have visited online seem to have the same parts system and none of them list the backup light socket.

Any suggestions would be helpful before I start in the salvage yards.