if it not possible to obtain a cylinder of nitrogen or argon (and the guys selling those cylinders know what they are being used for)
Yes, Argon is very commonly used for mig/tig welding. Nitrogen is used to charge tasty kegs of Stout, ala Guiness. I don't know what "guys" your talking about, but thats what the guys in my world think.
And the other alternate is Helium, which as we all know is only used by clandistine chemists as an inert atmosphere, stay away from that one!!!