Whether you use your cylinder for Diving or Airgun purposes you will need to get it refilled after it has been used.
You can get your cylinder filled from any reputable dive operation, the one requirement is that your cylinder is within the legal test requirement - This varies worldwide and by different cylinder types. In the UK the testing requirement is currently defined by the BS EN 1968:2002 standard.
What this means for you essentially boils down to this;
- Your diving cylinder must be tested every two and a half years to remain valid for filling.
- If your cylinder has a gauge built in to the valve it must be tested every five years to remain valid for filing.
You can read more on this through the HSE.