Twin XL sheets can generally only be found in the last summer and early fall because about 95% of twin xl beds that exist exist in college dormitories. For example, in August and September, you can find plenty of twin XL sheets at Bed, Bath & Beyond, even at Target. But any other time of year, you won't find them. Stores don't carry them. They find it a waste of shelf space because August and September is the only time anyone buys enough of them to make it worth is, which is because it's always parents buying them for their college kids, because if college kids don't have sheets, they're not above just sleeping on a bare mattress with a blanket, which of course their mothers are aghast about, but that college kid'll be damned if they're going to spend $40 or $50 they either don't have or would rather spend on beer on something as superfluous to them as sheets. It's capitalism. The free market has proven what I'm saying, which is why you can only find twin XL in stores right before fall semester starts and for a month or so after it starts, and that who buys them isn't generally the people who sleep on them but rather their parents.