Mattresses where we live are not offered in the Twin XL dimensions. We need to purchase sheets/duvet cover for our son. Other than PB Teen (did not love…kind of contrived?), where can one buy Twin XL online? We can have them sent to a friend in the US, so shipping is not the issue.
Thank you for suggestions. If it does not allow a link, just name the site and we will find it.
Amazon
If your friend has a Costco membership, they sell a few online.
Target, Ikea, Lands End
Amazon has lots.
Amazon, target, for something a little more trendy Urban Outfitters (last has a lot of floral type but also some solid/stripe combinations that a son might like)
Most stores online have them..
Beyond above - company store, brooklinen have twin XL
Are you outside of the US? My kids have twin XL at home, and we had no problem finding stores that sell mattresses or beds.
LL Bean are my fave. Remember that the fitted sheet is the only one that has to be XL. Duvet covers, pillow cases, even flat sheet etc are fine if twin.
On this, note many/most students like to buy a mattress protector too and obviously that needs to fit as well.
Yes, and don’t unpack this one until you get there! They are compact for shipping but expand - permanently- when opened.
Amazon for basic Twin XL sheets and mattress pad. For duvet, blankets, etc., if they do not like what they see in Twin XL, you can just do a regular twin or full. It just won’t have extra blanket on top to fold down or put under pillows when making the bed. A full will hang over the sides, which can either be good or annoying if you store things under the bed or are lofted.
Most have been mentioned here already - Amazon, Target, Company Store, Garnet Hill, LLBean, etc.
I will say that we bought PB Teen for my son and while they were on the higher price side, they have held up well through two years of dorm life and campus laundry service, so the quality and durability is very good. My daughter just chose a $19.99 pair from Amazon and I don’t not have as high hopes for those to last, but we shall see. She is also more likely to change her taste/cares more about the look and design of her room than her brother, so I will probably be buying her new color schemes every year anyway. 
Overstock/bed, bath and beyond
I keep forgetting BBB still exists since they shut down all their physical stores.
Overstock bought the name/contents
Great info. Thank you, all.
If one wishes to open it up to let the new smell off gas, is it really impossible to fold it in half and stuff it in the back of an suv? They must be foldable? We are otherwise light packers. Not lots of stuff.
You certainly can toss these sheets in a bag and be done with it…maybe after giving them a wash.
Back in 2003 and 2006, those XL twin beds were also thinner and the mattresses not very thick. Our kids had those jersey knit sheets which do stretch…and regular twin size fit perfectly. We happened to have those from summer camps.
To OP:
Many colleges allow students to ship things to the school to be held for your arrival. Some places like Amazon have delayed shipping so you can order in, say, July and have delivered in Aug.
Or, if child is going to college in a semi- big city, some of the stores like Target, Walmart (and formerly BB&B) have an in-store hold for college kids to order before arriving.
They get pretty big when they open and really don’t scrunch up much. Ours would never fit with everything else that was moving.