Happy The Man was released on the 26th May 1972, (thank you Phil Morris).
This is proved by evidence in the form of an advert which appeared in Melody Maker on Saturday 3rd June 1972, so from that I can guess its either
Monday 29th May or Monday 5th June 1972 for the release date.
This is the Italian release of the single, so the release date could be different.
Happy The Man (Non album track)
Released on the Phillips label
Catalogue number (6073 316)
(Many thanks to Chris Simmons for this rare single)