All roads point to Dalaran. Long as you have the bite to backup your bark (arena rating and such) you can go to the sewers of Dalaran and talk to a plethora of goblins for the gear.

• Zom Bocom, the Apprentice Arena Vendors, sells the blue set (Savage Gladiator)
• Zaxi Smolderpipe, the Arena Vendor, sells the epic set (Hateful Gladiator)
• Nargle Lashcord, the Veteran Arena Vendor, sells the best epic (Deadly Gladiator)

You can still buy the old brutal/vengeful stuff from the vendors in Outland, but why would you? Mind that to buy the new PVP gear you have to have arena and honor points. This is somewhat forcing players to play in the arenas if they want to partake in the new gear but I suppose that is offset by the fact that all crafters can create cloth/leather/mail/plate armor “sets” that have resilience.