Since it is a 2WD, size is not critical. What you are looking for is a good load rating. Generally, industrial tires give it to you. I'd go have a look at what your nearby Kubota dealer puts on the front of a tractor with similarly sized rear tires. My L3200 came with 27x8.50-15 industrials. Go for at least 6 ply rating.
You can get good prices on ebay, for tires mounted on wheels, ready to. Measure your center hub cutout, and the bolt pattern. They'll fix you right up. I personally like tuckertires.com; other threads here recommend other dealers.
You can also just go for the industrial tire that will fit your rim, in a 6 ply rating. Give them a call.
Nice looking tractor!!