From what I can see on Wowhead, I'd try Molten Core. It looks like your best drop rates come from level 58-61 rare or elites so that lets out most normal instances. So Blackwing Lair, Molten Core, maybe Upper/Lower Blackrock Spire. The problem with finding it on the AH is most folks with an item of that level would disenchant it and sell the mats instead of trying to auction hard-to-sell gear (since most buyers would just buy outland gear instead).

You might try this chest piece http://www.wowhead.com/transmog-set=270
It is almost identical to the one you are looking for, except it is mostly gold. I check the AH daily for several sets, and cringe when I think of the many pieces that are vendored.
There are several sets that compliment each other in that color scheme/mail armor.
Magnificent, Masterwork, Battleforge, Engraved, Glimmering...
I've used a mix of these armors along with the "stylin' crimson hat" (LW craftable) to achieve my desired look. The gun is from BWL and though you can't see it, the polearm is from trading in 50 clams to the Murlocs in the Borean Tundra. Same skin as the one dropped by Sulfuron in MC.
http://us.battle.net/wow/en/character/trollbane/Pandi/simple
The turtle pet, Terrorpene, completes the look quite nicely.