Mike,
The Missions are no longer made, so you for sure won't be getting a Mission replacement.
Not sure what rig you have, but if you have 6,000 lb axles there are tons of alternative tires, including many of the LT series american brands. If you have the 7,000 lb axles and you want to retain that capacity for hauling, the selection gets very lean. The only American tire I know of is the Goodyear G series.
LonnieB is a good resource, and I hear he keeps a cold one in the fridge of the shop for any MOCers that pull in for new skins
. You might PM him for advice if he doesn't jump in (to tell me I'm full of beans about the cold one anyway)!