check out Onidea suzuki. I got mine for 169, that was both seats too...they have a web site. also if you goto your local suzuki shop and have them look up the price on onieda, they will probably sell it to you for the same price.
You could also post a WTB front gel seat in the for sale section. But they are only sold in pairs. I would think that you could find someone to just buy the rear Gel seat. I think a member named Rstew was looking to buy a rear Gel only.