Motorbike shops, especially those catering for the custom/cruiser fraternity will probably do you a variety of bandanas or "outlaw" headgear. Try Hein Giereke on Gt Northern Road - It has plenty of gear like that & I think I remember some "pirate" stuff but it ain't cheap.
McGowans (or whatever its new name is) off the George St/Hutcheon St lights had some of that upstairs when I was last-in. Bikesafe on King St too - Again, last time I was in there, I was horrified by the sheer variety of strappy/frilly leather on offer. More than your average fetish-shop!
Eyepatches, peg-legs etc, I have no idea! Maybe some of the artisans at a re-enactment meet could be persuaded to knock some up?