well up to rank 30 the purple roots hiding in the waters in ysigrath flushed me out pretty regularly. There are also purple "violet explosion" potions on a gnome in darien or dagdan or whatever, but think they suck.

Really the trick is to find the random spots in areas where people can't camo hide and wait for their overly aggressive asses to walk to you and step out. If you have the patience for that kind of thing.