If you do use those Oxygen tanks - for compressed air - you might only need to use diving and paintball fittings/regulators/QUOTE]
Those tanks are specific for the use of oxygen and have a valve that is designed for oxygen only (pin index or a bullnose din), so that you can only use them with a oxygen compatible/ oxygen serviced regulator which is double the cost of a normal paintball/dive regulator. Plus the fact is that a normal dive shop who's doing refills need to have a converter if they want to fill those oxygen tanks with normal air.
And don't even think about to use oxygen for your airbrushing, you might need an adaptor to replace your hand in the future doing so!!!!!!
LOL not suggesting he use O2 at all
I remember now that you are right regarding the fittings. I also know that her in SA you can swop out any type of tank when you take it to be filled - so if I took my oxy acetylene tanks (for example) to the gas supplier, they could (and have) replaced them with full CO2 tanks. problem solved
Although you would still need to pay for the full CO2.