That is why I always carry two spare tubes on a bike tour.
Boy! Me too!
I usually take 6 complete tubes (plus as many patch kits, both instant and self-vulcanizing as well as a tube of beta-cyanoacrylate super glue, some tire boots, and dental floss) on my desert tours (augmented with a pair of Mr. Tuffy liners I install once in goathead thorn country -- they have worked well for me).
Unfortunately, 6 spare tubes were not enough on my 2010 Great Basin tour, when *all six* failed by valve pull-out, some as I was pumping a little air in them to hold their shape outside the tire. One was an IRC from Japan, two were Specialized from Taiwan, one a Vredestein I bought in Rotterdam, a Michelin from France, and a Continental I got from Germany. All made at different times, but the production/date codes indicated they had been made within the prior two years. All had been stored in cool, dry places in plastic bags to prevent UV/ozone degradation. All had faulty vulcanizing 'round the valves. Not had such bad luck since.
I'd "closed the loop" on my tour, but had to call for a "rescue ride" by car the last 150km home. Oh, the ignomy!
There were no bike shops or stores where I could purchase tubes.
Best,
Dan.