On Wednesday, July 17, 2019 at 2:58:01 PM UTC-7, Geoff Minors wrote:
Wanted O2 Cylinder about 22" long total X 5" Diameter.

Your best bet is to choose a standard size medical cylinder, then have it fitted with a CGA540 valve to adapt to standard aircraft oxygen fittings. Most of the places that sell medical cylinders can do that for you.

Standard size chart:

https://www.tri-medinc.com/page12.htm#cyl-spec