The stockers aren't available yet, but you can put any 2.8 rims and tires on the volcano or Tsunami vehicles.
Like these.

[link=http://www.allaboutfunhobbies.com/products.htm]http://www.allaboutfunhobbies.com/products.htm[/link]

[link=http://www.allaboutfunhobbies.com/images/Tires 20and 20Wheels/PreGluedTiresandRims/tra3668.jpg]http://www.allaboutfunhobbies.com/images/Tires 20and 20Wheels/PreGluedTiresandRims/tra3668.jpg[/link]

Any style of 2.8 rims and tires will work.