A lot of welding shops would source the tank for you. I suggest you buy a quality regulator, if it's expensive it's worth it. The tubing I got was PVC tubing
https://www.amazon.ca/dp/B09L5KCC1X?ref=ppx_yo2ov_dt_b_fed_asin_title and you just gotta make sure the ID of the hose matches the nipple attached to the regulator. The hose should be a good length, mine was 5ft but you may need shorter or longer, ideally not going over 6 ft. I'm confused with what you're doing with the bag, are you duct taping it shut, or are you fastening it with the elastic and toggle?
Yes, upon looking properly I found Argon, which to my understanding works the same albeit being heavier than nitrogen as a gas.
I think I'll buy the regulator from the same shop, no reason not to. At 52€, it seems not as expensive as some of the oxygen regulators I saw, but not cheap either.
As for the bag, the idea is:
1) Lay bag flat.
2) Roll over about an inch of the opening outwards all around the bag, tape it against the surface. This creates a small hem.
3) Cut a small hole at the bottom of this opening, thread your elastic around
4) You now have your elastic running the circumference of the exit bag, coming in and out both of the hole you cut into your hem.
5) Use cord fastener onto it, like a hoodie cord closer. Which it is.
It's meant to emulate exactly that, as far as I can tell, but since I (foolishly) tried it with a mask before, I've yet to build it.
Looks like this in the PPH:
(The small rectangle is the attaching point tape for the tube, best I can tell).
Are you just using an elastic as is around the base of a turkey bag, or did you build your bag yourself?