Hey Larry
There is a guy in Kansas that has a large stock of new and used reducing rings. Dan Cavilieri /Cavco Sales.
he has a very good supply of any sunnen replacement parts in stock. He is my go to guy for anything sunnen 

If you have the numbers for the support rings give him a call. Also you can try Jon at Jamison equipment in Iowa or Sam and Don at Farris equipment in Texas.

All of those guys are great to deal with and no junk stuff either.

There is a few other equipment dealers that have ebay stores that would be worth looking at as well as the aforementioned as well but call them on the phone with you needs as they have told me they get inundated with emails and it can take quite a while for replies depending on what you need.

Hope that helps

Dave