Well now, I see that this Ventrac page has a lot of traffic! LoL. I'm in Ohio and looking for some replacement used wheels for a 4200, wheel size 8x8.5 five bolt circle on 4.5 inches. Its always good to have a spare, unlike my BMW with run flats....
Have you checked back with your sales rep to see about a replacement? Tractor supply and a number of other outlets also have tires and rims you can match up to what you are running on your unit.