Scarlet Crusade Hidden Transmog

The Scarlet Crusade Hidden Transmog can be purchased from the Scarlet Quartermaster, an NPC found on the Darkmoon Island during the Darkmoon Faire World Event.

/way Darkmoon Faire 58 80.6

Scarlet Quartermaster

At first glance the https://www.wowhead.com/npc=108785 raises some questions about her intentions. However, if you interact with her while wearing the https://www.wowhead.com/item=23192, she will offer you the option to purchase transmog items.

Tabard of the Scarlet Crusade

https://www.wowhead.com/item=23192 drops from Armsmaster Harlan in Scarlet Halls. The drop rate seems to be around 1%, however you can farm this on normal again and again until it drops.

Note: You don't have to wait for the Darkmoon Faire World Event to be active, you can farm this item whenever you want.