Cryptstalker Armor

Cryptstalker Armor is the tier 3 hunter set.

Source
In Mists of Pandaria, this set can be bought from the Black Market Auction House.

Prior to Wrath of the Lich King, most tier 3 items could be acquired through quests given by Huntsman Leopold, who was found in Light's Hope Chapel in the Eastern Plaguelands. Before the quests became active, Echoes of War must be completed.

The quests required several crafting materials, Wartorn Chain Scraps (which dropped from Trash Mobs in Naxxramas) as well as a token from a boss in Naxxramas

The only exception is the Ring of the Cryptstalker, which dropped directly from Kel'Thuzad in Naxxramas