the bearings are 6206-zz
they're available elsewhere, but generally speaking kubota is less expensive than most everywhere else (unless you buy them in bulk).
You can also use 6206-2RS which is two rubber seals rather than metal shielded. The shielded bearings do a little better with high shaft speeds than RS, but RS protects against dust/dirt a little better.
koyo has a neat little calculator on their site (IIRC) that deals with expected lifespan given the rpm and loading. Worth a look if you have the data. Remembering, radial ball bearings don't do all that well with axial loads (side loads). You'll see this if you look up the specs. And rotary mowers do in fact load the bearings significantly in the axial direction. Woods used a lot of tapered roller bearings in their finish mowers, and they were rare to fail-unless owner neglected greasing them. Power hungry though. Always a trade-off.
Koyo has lasted longer than the OEM bearings, but the OEM stuff is dirt cheap and I don't mind buying them for that reason-I actually keep 9 on hand at all times, buying from the dealer. My dad used to be a dealer for Fafnir bearings-which was a division of Textron (he had a home-based bearing shop)-until they sold out to Torrington in 1988 (?). Torrington sold to Timken as I remember but I don't know what year that took place, we moved in 1989 and left most of that stuff behind.