Try your local fire extinguisher people.Over her they sold me a retested Co2 cylinder with the correct fittings about $35 another $15 to fill it ,then only about 15 dollars a fill for 10 years for another retest,probably a bit dearer these days,often these bottles can be purchased out of date for free or $5/10.
If you use MIG I believe that CO2 is the best way to go,a bit more welding spatter ,slightly stronger and a lot cheaper than BOC or anyone else.
And consider Oxy/propane(LPG)and straight propane for heating,instead of Oxy/Acetelene.David
