The Korum chair brackets work well, but be wary, they aren't too strong - I broke one recently and found that the housing for the tightening nut is plastic.
I have the Middy Star-grip which too is ok, but in my experience parts are too easily lost.
I do note the ideas that this chair is intended to be lightweight, that said, on rocky banks, towpaths and concrete slabs where one can't get a rod rest in a chair adaptor is a godsend. While I'm at it, consider a small side tray too - not having to perch tackle boxes or tubs of maggots on rocks or in bankside crud is something worth considering and both items weigh next to nothing.