I made one out of a copper uni-strut clamp. I can't find it now, so I don't have a picture. It started out as this:
I cut both halves narrower, and bent up the tabs(the part that hooks on the unistrut). I drilled holes in the tabs for the cage to bolt to, and then cut a strip of rubber to pad the bars with. It isn't the most decorative piece,but worked like a champ.. til I picked up a bike the had a store bought unit.
BTW, I had the Strut clamp already, that's why I used it. If you want one send me an address and I'll mail it out.