Why go to the expense? Make your own. I did and it works great.
This was actually a pic I took for my UDS build, but if you look behind the UDS to the right, you can see my weber kettle with the rotisserie ring I made.
I took a section of drum, cut it at the "roller flare" to create a flange, cut some 2.5" slots for the spit and mounted the rotisserie brackets.
I used it the other night on the UDS to do a couple of chickens. Including the cost of the handles, the thing cost me about $10.00 to make.