John deere 14sb drive wheels

I have a John Deere 14 sb that my father purchased in 1989. Kawasaki engine (green deck).This mower is about bullet proof. 25 yrs old and still starts on 2nd pull. The rear drive wheels are about wore out and I am unable to find to find relacements anywhere. John Deere part # 104851. JD says it is no longer available. I have pulled the rear wheels off and the drive gear for the wheel is actually a molded gear all the way around the inside of the part of the plastic rim. Not the tire but the YELLOW rim. None of the replacement wheels for the 14 sb even show this type of gear(wheel) any ideas?