Originally Posted by Technosavant
You can get them from just about any tire shop or order them from the Tire Rack. Warning: the Mopar ones from the dealer aren't cheap; I had one on my winter wheelset (from Tire Rack) crap out on me, and the dealer replacement was $100 plus labor (was headed there anyway).
You're right about that. They are not cheap. I've already had to replace one of mine. I had a slow leak in one of the tires. After taking to Firestone, it was the rubber valve stem that had split. Including parts and labor, it would have been nearly $50 to replace. But they offered me the road hazard warranty (since I had bought the tires within the past 30 days) and I decided to spend the extra few bucks for peace of mind.