The items out in the world (Marshals, Grand Marshal’s, High Warlord, etc) that use the level 60 PvP art are un-transmogrifiable (including the item level 115 stuff that shares the name from Burning Crusade).

In Area 52 a set of vendors has replaced the PvP Vendors who used to live there. Grex Brainboiler, Krixel Pinchwhistle, Tini Smalls, Kezzik the Striker, Big Zokk Torquewrench, and Leeni “Smiley” Smalls. These vendors sell new, transmogrifiable versions of the classic armor to players who have the Feat of Strength for Legionnaire/Knight-Captain or higher under the old PvP system.

There was a bug with the Feat of Strength granting access to these items, but was hotfixed within the last couple of minutes. If you meet the criteria log out and back in and you should be able to access the vendor.

The design intent with the Feat of Strength achievement requirement was specifically to limit these particular art styles to players who earned them through the OG (and relentlessly difficult) PvP honor system, while keeping the door open to reward them to more people in the future.

In a future patch the items sold by the Area 52 vendors will also be renamed ‘Replica of’ to be more consistent with the items sold by the Darkmoon Faire – they’re currently exact duplicates of the original items that allow transmogrification, which is obviously a bit confusing.

Potentially related, since he’s in the same area, Kezzik the Striker sells inaccessible Season 1 Gladiator’s, Season 2 Merciless Gladiator’s, and Season 3 Vengeful Gladiator’s gear to all players, as the majority of that gear didn’t have restrictions.