clamps like this are all over ebay. You need an accurate OD meaurement of your seat tube.

Try to find a clamp that does NOT have the bolt threaded into aluminum, but instead has a floading nut that can accommodate the angle change as the collar tightens.

DiTBho you paid a lot for that seatpost. The clamp bolt is real easy to damage if you are tightening it with a pipe wrench or channel lock pliers. Find yourself a really good 6 point box wrench in 13 mm to avoid damaging that bolt. You can also use a 13 mm socket, recommend a Snap On SFSM131. Replacements are hard to find and expensive.

/markp