I buy from my local farm store that carries lawn tractor tires. Have no brand preference as they all seem to perform the same. Around here, the key is to make sure that someone can install them. Oddly enough, our Walmart installs, but didn't have my size, and the farm store sells, but doesn't install. Go figure. Between the two, I got it done.
Recently replaced a front set that had been in use since 1997.
I have a pair of tires on a 1987 (bought new) 8 HP dual stage snoblower. They are the original tires. I spray them with silicone once a year and store the snowblower over the summer with the weight off of the tires.