If you go to the Hustler website, hustlerturf.com on the bottom of the page is a link that says manuals. look up your model number and it will give you the parts breakdown.
In section 5-2 it shows the tire being a 11x4-5. Simply measure the gap of the front fork and you should be able to find an aftermarket flat free from there. Don't blame you for going flat free, those little tires are a bear to fix. You'll get a bit rougher ride though.