I got mine at zdmak tools -
http://www.zdmaktools.com/wbstore/main.asp?action=PROD&PROD=M0093B&CTMP=1
works great and I like 2 features it has:
1. It can be tightened to the canister to prevent slipping using the side 12mm bolts.
2. It has either a 3/8" and 19mm hex for using either a box wrench or a socket extension and drive - great for getting a torque wrench on it.
$13.95 + $7.00 S/H - $21.95