Mato Toys is the only distributor that has the "Super Version" HL's, at least according to what I've read in this forum.
This post makes mention of what it involves (just the metal gearboxes):

http://www.rcuniverse.com/forum/m_4150676/tm.htm

Maybe you might consider ordering the tank from them--then you will get it all at once.

-Harq