If you're just replacing your original turf tires, check with forum vendor Miller Tire. They should be able to get them, and their prices are very competitive. I haven't bought tires that size, so I don't know what the average price is.
I've always bought my tires locally. If you're in Middle TN, check with General Tire in Gallatin. Ask for Rob or Roy on the truck side. They put tires on several pieces of equipment for me when I was down south and their installed, out the door price was less than I could buy just the tires for online. I don't have specific recommendations for other parts of the state, but check with your local dealer for a suggestion. Car tire shops can't mount tractor tires with their machines, you'll need a truck/ ag tire shop.