Go here

http://ecfr.gpoaccess.gov/cgi/t/text...4/14tab_02.tpl

and search for "oxygen" in Title 14. Part 23 has a number of
citations for supplemental oxygen flow rates and stuff like that.

Google "aviation oxygen". There a number of sites that only deal with
aviation O2 systems. One or more of them should be able to service
your regulator.