Perception teams up with Harmonygear.com for outfitting and accessories.
You can try their Rudder Kit #G, which is specifically stated to fit "Dagger & Perception Tandem Touring, SOT and Rec Models with molded rudder post hole at stern of boat."

Retails at $225 from this site :
http://www.harmonygear.com/product/203820/RUDDERKIT_G/_/Rudder_Kit_%23G_-_Dagger_%26_Perception_Tandem_Kayaks

Backcountry.com carries Harmony items but unfortunately does not have the rudder kit.

Hope this helps.