I bought one made by TSS a few years ago - this has the lips to stop the kush drives coming out. I bought it from a place in Germany "Ducati Shed" which no longer seems to be running.
It's a copy of the Talon one, I believe, as the same sprockets fit, but you can also buy TSS sprockets to match.
I had a quick Google and found this:
http://www.sebimoto-germany.de/engli.../tssducati.htm Looks about the same prices I paid.
Picture of it on the bike here:
http://horrible.demon.co.uk/748/slides/DSCF0503.JPG