How about a helix one Ed?
They do 1" and 1 1/8" replica's
http://www.helixbmx.net/seatclamps.htm
I emailed them a while back and they said they are closed now and everything is sold out.
If you do a wanted on the bmxmuseum you could probably pick one up up.
If you are going to make one an SR MS422 would probably be the one to use, right shape and cheap.
