50catching the merchant
Only the Traveling Merchant carries this one. He turns up some mornings with a small random slice of a very long inventory and packs up at dusk, so the set is a matter of checking him every visit rather than saving toward a known purchase.
If the uniform or the pants are on him, buy on the spot. He holds nothing for later, and the next arrival may carry none of it. Multiplayer worlds help here, since more players awake means more chances to catch a visit.
wearing it
It is costume only, worn in the social slots over live armor. The natural home for it is the cooking side of the game: a kitchen room in a town build, or the person standing at the pot handing out food buffs before a boss.
The hat's flavor text is a nod to Gordon Ramsay and the volume he tends to cook at.