I work for a small technical school and mentioned one day to some of the staff that our students would greatly benefit from some sort of professional/workplace etiquette classes, as they were learning their trades, but not learning how to comport themselves professionally for interviews, etc. The first thing they said was, "Who in the world would teach a class like that? You?"
It seems like there is a real need for this, and like you, OP, I have no idea where one would get credentials for that sort of thing. But wow-wouldn't it be so useful!