Maybe make You a platform or box and as Notmyname mentioned...put a swivel Boat seat on it?
There are some Ladder Stand Companies that make a swivel type seat that sits on their ladder stand platform....bet You could buy one seperately and mount in on a piece of steel or sturdy square piece of treated wood?
Check out the following to see if You can buy a nice Swivel Seat set up from the following companies and look in the "Accesories" or Parts Replacment Section?
www.bigdogtreestands.com
www.biggametreestands.com
www.sportsmansguide.com
www.rogerssportinggoods.com
www.summittreestands.com
www.apitreestands.com
www.olmantreestands.com