This seems to change. When I looked about a month ago to buy a spare I noticed that a lot of places were our of stock. You will probably need to do a lot of checking. Here are some places worth looking at that sell Zilla packages:
When I bought mine the cheapest was motoxmall. Good luck.
Check out Interco Radial Reptiles or Swamp Lites along withe Remington Rims at "Discount Tire Direct" on-line You won't beat their price anywhere. The Interco tire is better than the Maxxis tires, and the Rem's are certianly better than the STI's wheels!!!
PS. This off course is my humble knowledge!!!!!!!!!!