His outfit is literally in the game.

The exact version is a random drop from the level 60 dungeons Sohr Khai and Hullbreaker Isle (Hard) as gear for MNK/SAM, with a recoloured version for NIN, and you can buy a dyeable version for those classes on the marketboard also at level 60.

There's a healer version of it as well from the level 61 dungeon The Sirensong Sea.

If you're at a lower level or different class, the Thavnairian Bolero is a good start for looking similar, then have a browse through the marketboard for additional pieces you like.

Also I'm guessing you might not have cleared ARR yet, but you get one appearance-changing Fantasia potion for free when you "finish the game" and reach the credits.