Paul Farquhar
Legend
Off the top of my head without my Greyhawk material in front of me, I don't know. I'm sure someone who actually works on D&D for a living could think of some that are appropriate. Let see... a monk Archetype for the Scarlet Brotherhood might appeal to some players. Knight of the Great Kingdom for Paladins (or Fighters). Stuff like that.
The thing is, canonically, monks of the Scarlet Brotherhood are vanilla monks without any special ability. The Knights of the Great Kingdom are just an organisation - again without any canonical special abilities. You could make subclasses based on them (banneret /Oath of the Crown are fine for the Knights) but the setting doesn't need them. And it seems to me that most of the people who want Greyhawk don't want any changes made.
One thing I would do would be a bard subclass with close ties to druids. The current bard is very different to the 1st edition bard which you would expect to find in Greyhawk.