You might also consider getting one of those automotive air
tanks - you know the kind that you fill at the gas station
(or from your own compressor) and keep in the trunk of your
car to fill tires.. These go for about 20$ starting at 5to 20 gallons.
These are just small compressor-like tanks- not the 12v tire
compressors (which could be very handy fill them indoors if
you don't have a compressor at all - and they go for 10-20$).
These already have a "tire" type filler valve, regulator, pressure
gauge, coiled plastic flex hose, and cleaning nozzle. Perfect for
touching up pain scratches etc when used with an airbrush..
Another alternative might be those pressure canisters for
fountain pop dispensers - good to 120psi only, but you'll have
to buy the regulator, hose etc. I considered refilling an old
extinguisher bottle, or spent propane (small welding cylinder)
but changed my minds after reading all the warnings and threats
of imprisonment for doing so. I would have preferred a more portable
thermos flash sized unit, bit opted for an under-bench automotive air tank.
I still loathingly buy the pricey, noxious, smelly pseudo-chloro-flouro
"compressed air" cans sold for computer cleaning.. but now with the tank
I'll be using them less. Those canned fumes can't be very healthy for you-
read the warning on the can about using in a big room, heart attacks etc..
h