Here's Seats that fit the Nightrod Special's they will fit the Muscle but you have to change your rear fender to a Nightrod Rear Fender 2007-2011.

Here's the page to read about those fenders: https://www.grcustoms.com/index.php?route=product/category&path=248_285

Just skip down past the SOLO FENDERS as they Won't Work with These Seats Either!