These are two really good examples I didn't consider. I'm not sure if I'd call them 'left-wing' in terms of fans, but they both very much exist on a 'people against big business' basis.(Original post by KingHarold)
Probably AFC Wimbledon.
Real Man U supporters probably (those in Manchester or brought up there, not the plastic glory seekers who probably have no political opinions).
UPDATE: When you said Man U for some reason I thought you meant FC United of Manchester, not Man U. My bad.
... and the ones that won't