There'd be specialist companies that do bulk oxygen supplies too, a quick search found things like https://www.dswgascylinder.com/product/liquid-oxygen-trailer.... Not a market I'm familiar with.
I suppose I'll just add in postscript; your not going to get much out of the conversation if you don't take it seriously. There are people who make great money selling oxygen. It isn't automatically priced at $0. In some hypothetical world where quality oxygen wasn't just floating around in the atmosphere, people would pay for it in the same way they pay for other essentials like food or water. Paying for water is about as crazy as paying for oxygen, they both basically just turn up out of the atmosphere. And there is precedent for a commons essential good becoming more expensive, food used to be something people just picked up off the ground for free. Or hunted down on unclaimed land.