The bearings in my spinner are 7/8" O.D. and 3/8" I.D. by 11/32 thick. The local "Bearing Distributors" in my town sold them to me. I think they are Japanese. You need to have high speed bearings, obviously.
Someone else mentioned using 12L14 for centers. I would advise against steel centers. Wood, plastic, or brass would be much easier on the barrel.
Bill Jacobs