Gary...If you cannot locate one....make your own....looks like the base is a plowing disc..and the shaft looks like a 3/4" pipe. A good welder could weld the two without any problem...
The frame looks like a 3/4" or 1" by 1/4" thick flat stock iron. Any good machine shop has this and they can also bend it in a circle...Have it sandblasted, powder-coated, and
there ya go...Just a thought....Warren