If they don't sell the kit that way you could order additional drums through your dealer. The new Mods are offered in the Legacy, Classic Maple, Keystone and Clubdate series. Check out the Ludwig website.

Although not a Mod Orange wrapped drum, I just ordered an 18" classic maple floor tom through Forks Drum Closet. It was an easy process and Forks' price was lower than 3 other dealers I contacted.