Going back to the mid- and late-70's, you've got manufacturers like:
--Goodman's (LA-based. Made the Flyers, Islanders, Kings and the original Canucks' "flying V" jersey during the 70's. Note the number font on the Isles, Kings and Canucks jerseys from the late '70's. It's identical)
--Rawlings made Penguins and Blues jerseys during the mid-70's.
--Stall & Dean was the Bruins' jersey supplier during this period. The Penguins eventually transitioned to S&D from Rawlings. S&D also made the first Pens' black-and-gold jersey, much to the consternation of the Bruins!
--In the late 80's, Pittsburgh contracted with Century Sports for jerseys. There are likely pics out there that show the hem tag.
--And there's Gerry Cosby, of course... they supplied the Rangers and (in the beginning) the Devils for years.
--Gunzo's supplied the Blackhawks for many years as well. (That was a great jersey tag.)