If you are in the U.S., AirGas or similar welding supply stores will sell or rent you the O2 tank as well as fill it. For the air filling kit, which includes the hose, regulator and flexible nozzle, check out Air filling kit which is where I got mine 10 years ago (wow the price has gone up).
I got mine from the local welding store. The air fill lines from Pentairaes are garbage, leaks around the fittings. If you leave the oxygen on it will leak out. I need to find a better one.