If you go to Kohler’s website, under the parts locator you can find replacement hinge sets, unfortunately you have to purchase the hinge replacement kit that has new hinges and covers/caps. This is cheap compared to buying a whole new seat. Hope this helps.

http://www.kohlerserviceparts.kohler.com/SearchResults.aspx?itemtype=servicepart&searchparameters=hinge&pagenum=0&pagesize=12