They've closed the store, you have to call up Activision's support and tell them you want to order a new dongle. They'll send you an email with a confirmation link and some other information, then you *have* to send them a check with the info for $15. Takes 3-6 weeks for delivery supposedly.
If you want it now you pretty well have to buy a new controller, though, if you check ebay you can find some great deals on the full bundle. Like 14 bucks for the game and controller with free shipping.