I am not a pneumatic's person myself but as CO2 is far better in this regard than air, this is manly due to its stability as air is (as you know) is a mix of gasses and will not compress to a liquid. (evenly at least) CO2 will do it reliably and consistently.

Even better for this is nitrogen, that is capable of even higher pressures (3000psi +) when it goes from liquid to gas. but it is also illegal to use in machines over here for that very reason. It could easily blow most systems apart.

We have a 10 bar pneumatic set up for an axe robot and even at that now pressure I know if I make a mistake it could be fatal.

As for filling, we have a massive CO2 tank in the garage, in the same size tank you have for argon when welding. Basically a filling station. You may need a few adapters but its not that hard. But never go making your own! And most people use fire extinguisher tanks here as the ratings are known and they are designed to be safe from the outset.