Weaver compact tractor parts in PA. I bought 2 in July 2017. I believe you will find the OEM rim is actually 11 inches as was the case w/ my 1620. Stamped on the rim, don't go by what is written on tire. If you wish to reuse the center, if not damaged, you can buy just the rim, I did that as well, cost $ 100. The rim w/ center, used, VG condition, I paid $ 250 each. Did calcium damage rim? Why are you replacing?
I have two OEM rims + centers with new carlisle turf tires sitting in garage. Just haven't gotten around to mounting on tractor. I also have the spare rim, no center which I do not need.
Any large AG Tire dealer can order rim only, from this company, Remember, your rim is 11" not 12"