Recently bought an L2900 4WD. It has well used 27x8.50-15 R-1 tires on the front and 41x14.00-20 turf tires on the back. I wanted to put new R-1's on the tractor but unable to find 41x14.00-20's in an R-1. Other than a dealer, where can I find either this tire size in R-1 or rims for the rear...