The Pirelli 305/35/22 aren't discontinued, they're just back ordered. Pirelli has stated on another forum that they will start new production of that size in March/April.
I know they are available in Canada at a few retailers....PCM Tire in Quebec for one.
It looks like Summit Racing in the States also has them.
Vredestein is also still making their 305-35-22.
Michelin is also coming out with a 305-35-22 in the Pilot Super Sport.