@Kefrem I don't know the name but I know its the Mail set from the Ny'alotha raid.
Here's the link to the individual names of armor:
https://www.wowhead.com/dressing-room#fz80z0zJ89c8a8I8s8c8q838b8zq8fh8M2Q8d8zu8fu8M228sc8zya8MEt8wUK8fG8M3k8k58zdN8zYw8dAG8Mx2877iYOg8zpa8YOl8zpa87MYOv8zpa87mYOC8zLO8YOB8zLO8YOF8zLO8YOD8zLO8YO58zLO87a
If any set or piece of gear is not from the original vanilla WoW, TBC, and Wotlk, chances are you acquire it one of two ways:
Bazaar tokens. You can buy in game from other players for in game gold on auction house or trading them directly. Or you can purchase them with real money on the webshop from Ascension. There is a rotating vendor in the auction house area of each faction's capital that will occasionally have what you're looking for in exchange for the bazaar tokens.
Some features in game like Trials and Challenges will unlock appearances that you normally couldn't get in the base games. Check out these on Stony Tark, the Trial Master that can be found in every starting zone, or in your capital city.