There's two Mythic Americas Warbands that you can now pre-order over in the Warlord Games webshop for Warlords of Erehwon. They're the Tribal Nations and the Aztecs, and they put together everything you need to get playing either of these factions.
From the article:
The Tribal Nations can call upon the power of the newly re-boxed Sachem Warlord, Medicine Man (with included magic cards) and Wolves.
The Tlalocan High Priest, a powerful spellcaster flanked by bound dead, is re-boxed in a new set - which now includes the Aztec factions magic cards.