Because DHL has exited the domestic US shipping business, my company's mail room is throwing out the now-useless DHL packaging. Consequently, I now have ten DHL large poster tubes, and can get a dozen or so of the smaller ones. These are the boxes that fold into triangular mailing tubes and can hold a fair number of posters. I've used them in the past to transport Match Game SF and various bid and convention posters, including the Bay Area in 2002 posters we took to Australia with us. Being triangular rather than round, they don't roll away. You can check them as luggage, and while I have carried them on-board with me, I don't recommend it as they violate the "sizer" box rules.
If you're someone who can get to a BASFA meeting or otherwise physically meet up with me, let me know if you want one of these tubes.