Every mathematician worth their salt knows of The Acme Klein Bottle Company, although I'm one of the few I know who has made a purchase there; specifically, a question mark as a wedding gift to the former proprietors of a Seattle restaurant. (Some are more familiar with the proprietor as the narrator of one of the world's first cyber-espionage stories.) The business has diversified since my order five years ago, having extended to include knit wool hats with zero volume. Now absent from the site (although I swear they were there the last time I looked) are matching Möbius band scarves; fortunately, this need is filled by other resources on the web.
A new foray into the realm of one-sided wearables (brought to my attention by the pillar of hipster science) is the Möbius shoe, pictured below. Of course, to make the outfit work, one would need a matching Fortunatus' Purse.