5getting the pieces
This is developer gear, and developer gear only comes out of boss treasure bags. That means an Expert or Master world, because a normal world never produces the bags at all. Any hardmode boss can hand one over, with Queen Slime the single exception, and the roll is uncommon enough that a full outfit usually takes a long string of kills. Nothing crafts it and no NPC sells it.
what you actually get
The helm, the shoulders and the greaves are pure appearance, so they belong in the social armor slots on top of whatever you are really wearing. Watch what else falls out of the bag, though. FoodBarbarian's Tattered Dragon Wings arrive with the clothes and those are a working accessory, not vanity. The look is a horned, fur draped barbarian, drawn up for a production assistant on the Re-Logic team.