I wonder if one could even find a boot large enough to cover a 6"gash now days. Used to be, one could find them at the old country stores as just about all of them had services to fix a flat. NOW you rarely see a country store or even find an air or water stations at the city gas station and if you do it is for a fee. I would say that maybe half have windshield cleaning stations that are functional, meaning fresh cleaning solution, paper towels and squeegee /brush.
There must be vulcanizers around as there is all kinds of re-cap tires for sale. Likely they might not fool with fixing a tractor tire.