Here is a righting pole that I installed the end of last year and I have not used it yet. I tried the cheap alternative for mounting on the dolphin striker by using a bicycle goos neck. I hope it hold, but this is only compression forces and should be fine.
From hearing about another 21SC owner who made his own and then had a few problems. The main change is to thru bolt the cleats and pulleys thru the mast as the rivets with glass will mostl likel pull out. I can' wait to use it. Also, the cost was about $20 for the pulleys, cleats and $8 for the bike gooseneck. http://www.hobiecat.com/community/viewtopic.php?f=45&t=14627