Clockwork's Headphones can be located on the first floor of the Clothing Store. They can be purchased for 42 Bucks. After purchasing, you'll only be able to wear them in Adopt Me!, unless you buy them in the Roblox Catalog.
This item's descroption on the Roblox Catalog is:

Elite vintage headgear from the ROBLOX archives. These are museum-quality replicas of headphones originally made and worn by Clockwork. They are not for noobs...