There was a few threads about these a while ago. I shortly entertained the idea of adding a set of R1s to my fleet. Bridgestone makes a similar tire, but its in dimensions like a car tire.
Kubota has a part number: 6C072-50040
However, the dealer wants way more money than you can get them alsewhere, say M.E. Miller tire....
I looked at a B2400 with R1s prior to purchasing my B7610 with turfs. I thought they would be too rough for mowing duties, so I passed up machine. They were definitely taller than my turfs.
Do you need R1s or just looking at options?