The "Dungeon Set 1" armor was removed when Cataclysm was released due to the instances in which the items dropped became lower level. So now, set look-a-like pieces drop from the normal Burning Crusade dungeons.
Shadowcraft Armor - Dungeon Set 1
Mantle of the Dusk-Dweller
Vest of Vengeance
Shifting Sash of Midnight
Darkguard Face Mask