1catching the merchant
The Traveling Merchant is the only source, and he carries a random slice of his catalog on each visit. He turns up in the morning once your town is large enough, packs up at dusk, and takes whatever you left behind with him.
There is no way to make the outfit appear faster than checking his shelf every single time he knocks. If you see both parts, buy them on the spot. The next visit is under no obligation to repeat the stock.
wearing it
Jacket and pants, no headgear, so your head slot stays free for a hat or your own hair. Neither piece defends you; both are social slot only.
The look copies Kevin Keene from Captain N: The Game Master, a late eighties cartoon about a kid pulled into a video game console, and the tooltip lifts a line his mother says over the opening.