Dreadnaught's Battlegear

Dreadnaught's Battlegear is the tier 3 warrior set.

Source
Most tier 3 items can be acquired through quests given by Korfax, who can be found in Light's Hope Chapel in the Eastern Plaguelands. Before the quests become active, Echoes of War must be completed.

The quests require several crafting materials, Wartorn Plate Scraps (which drop from trash mobs in Naxxramas) as well as a token from a boss in Naxxramas.

The only exception is the Ring of the Dreadnaught, which drops directly from Kel'Thuzad in Naxxramas.

The set has since been removed, but was later reintroduced and made available in the Black Market Auction House.