FWIW, I emailed a person at the Iowa state government agency that regulates oxygen suppliers, just to find out what rules or policies they might have about adequately supplying people with CH. Didn't give any information at all about your situation, of course. Will let you know what I hear back. Not optimistic, of course, but you never know. There's a list of phone numbers at their website, too: https://pharmacy.iowa.gov/contact-us/board-office-staff
Unless one of your leads pans out quickly, I would seriously consider getting welding O2 to tide you over. An 80 cu ft tank will give you about 3.5 times as much O2 as an E tank. You'll need a regulator, and as has been noted, welding regulators bought at a welding supply place are typically expensive and typically don't come with a barbed adapter for mask tubing. If there's a Harbor Freight store near you, they will likely have one, and Walmart also typically carries them, or will ship them with two-day delivery. Amazon has a bunch, and if you're a Prime member you can also have two-day delivery (or pay to get it if you don't).