These are easy to make. The mounting plates are available on EBay and the metal strapping from your local hardware. I used neoprene sheet 5mm thick and sliced into straps and fastened with case fasteners. Also added guides to scope. See photos on my web page of a 10" and 8" mounting rings I made.
All held together with SS screws. I have an EQ6Pro guidance setup.
http://dsmithdale.net/dls006.html
PM if you need more info
If you want to spend more then try Tasco AU.
Dave Perth