I realize this wasn't the question you asked, but FWIW I use a 5 pound welding oxygen tank with a pediatric O2 regulator. At least on paper I can get ~10ppm in ~90 seconds @ 1.5Lpm.
I've used it that way over 80 times (including batches and starters) and I haven't even seen the needle move in terms of its capacity. I'm guessing it will last > 200 uses and then a refill is pretty darned cheap.
It's a little more money up front (and space), but for me it's one less thing to worry about (and costs less over the long run). Plus, you can hit your ppm target a lot faster than with an air pump.