Are you located in an agricultural area?
If so, you might be able to find a wheel and tire shop that's not 'proprietary'.
Here's the one I use:
Wenger Systems | (717) 656-9876 | New Holland, Pennsylvania
I realize you're not near this shop, but you can call them up for a quote, to get a starting place on price.
These guys have an inconsistent stock, because they tend to load up on dealer close-out surplus (read: CHEAP!).
I have oversize tires on my L2500, both front and rear.
For an R1 tire, you can't beat the Galaxy Earth Pro series, IMO...
I think that Kubota supplies Galaxy on certain 'tire on rim' sizes...
Mind the F/R gear ratio, when picking tires. Or, do not deviate from the OEM sizes.
F/R gear ratio on the L2500 is 1.6363.
If you're going to run an FEL all the time, you're going to want ballast in your rear tires.
Also, Galaxy is a subsidiary of Yokohama Tires.
Japanese tires on a Japanese tractor.
It's a natural...
-Paul