While this item may not have the claimed ~1.8% drop percent that Wowhead states, this armor is still in-game as of Patch 4.3.4.
As of 7-May-2012, the peak drop rate is only 1.2% and then quickly dropping to 0.7% and below.
While killing Infernal Warbringers in Hellfire Peninsula, two or three drops each of the Shoulderpads, Bracers, and Gloves in Felspark Ravine next to Thrallmar but only one instance of the plate chestpiece itself. This was done from a sample of approximately 450 or so Warbringers. I have not yet seen the Tarnished Mail Leggings or Boots drop so they may just have very slim chances.