Question about black market AH. What can appear there?

[Morae]

I just recently started playing wow again and I have been looking at BMAH everyday in hope of finding certain piece of item. I'm just wondering, if anyone of you could tell me how exactly black market works? What can appear there? Can nonset pieces appear there? Old content heroic non set pieces?

From my perfect set of transmog items, I'm missing one certain item with model+color that drops from 25man icc heroic. It is not part of a set so I'm wondering, if I will ever see it.

[IdTheDemon]

Tier 3 gear
Random pets from the Argent Crusade Tournament
509 iLvl gear from current raids
496 iLvl patterns
Random TCG pets, mounts and items
Various rare 1% mounts whether it's from a raid (Alysrazor, Invincible, Mimirion's Head, etc) or 5 man (Blue Protodrake, Ravenlords, etc) or the Green Protodrake and recently from 5.1 the Plagued and Rusted Protodrakes

As for weapons, the only ones I've seen are the Arcanite Ripper and the BMAH exclusive Sun Lute Axe.

[Tziva]

http://www.wowpedia.org/Black_Market_Auction_House

Complete list.