Where to find bushing for my Agway tractor/lawnmower?

On my Agway tractor (which also acts as my riding lawnmower) my left wheel's bushing is worn through. It is only plastic, so I guess it is understandable. I'm not going to go into too many details, but the tractor model is AGWAY LT 12/38. (12 horsepower, 38" deck) The bushing has about a 1" diameter. Thanks for any help you can give me.