Air fill options not necessarily in order of preferance are:
1) at the site you play
(may not be an option as HPA is not the standard for airsoft, but with sites diversifying it’s common for independant Paintball sites to run Paintball, airsoft and laser tag etc - look around to see if you have a suitable site nearby. Major chains such as Delta Force are likely to be geared up for punters only and run CO2, independent sites that take walkons will run HPA)
2) at an independent Paintball site
Sites give free fills when you play, and tend to be less keen on someone turning up just for air, as there’s no business for them to fill paintballers cylinders for use elsewhere - and the ‘customer’ could be up to something chavvy/unsafe. Pop round for a chat and you may get to pay per fill
3) at a dive shop. Even though they said they don’t fill Paintball they may be willing if you ask them about you bringing a fill adaptor.
Be wary that dive shops operate in bar and we operate in psi. No problem if they know what they are doing, but weekend staff have blown burst disks filling 3000psi to 300bar
232bar is approx 3000psi
300 bar is approx 4500psi
You would pay per fill, so pay the same for a small cylinder as a diver would for a large cylinder
You may be able to extend the hydro test timeframes on a scuba cylinder by having it marked ‘surface use only’ but check with the dive shop as they may not fill surface cylinders
4) via a dive cylinder. Buy a scuba cylinder and a fill rig. Get the scuba cylinder filled at the dive cylinder then use your fill rig to fill your airsoft cylinder.
This is expensive up front, but you then pay per fill at the dive centre
Only part fill you airsoft cylinder to less than the scuba cylinder.
Every time you fill they try to balance out the pressure, if you have a 232bar / 3000psi scuba cylinder then by fitting your airsoft cylinder that 3000psi of air goes into a larger area capacity across both cylinders which means the pressure drops, if you empty it then fill again the overall pressure drops etc. Keep going for maximum fills and then using it all then you lt scuba cylinder loses pressure fast sending you back to the dive shop to refill
Instead stay low, fill the airsoft cylinder to 2500-2800psi, which means the scuba cylinder keeps a higher pressure. Don’t wait until the airsoft cylinder gets low - if the site will let you then bring your scuba cylinder to the site when playing and top up between games which will preserve the maximum pressure in the scuba cylinder for longer
For more expense and maximum fills buy two or three scuba cylinders and cascade from them - 1 for main fill from empty and the scuba will drop quickest, 2 for a top up, and possibly a 3rd to maintain almost 3000psi
If you get a regulated fill rig or are very careful) you can use a 4500psi scuba cylinder to fill a 3000psi airsoft cylinder and get full 3000psi fills for a long time
Ask your airside site and they may bring in a scuba rig themselves for HPA players
5) via a stirrup pump
This will give you lots of ‘free’ fills but take time.
You will grow muscles and learn how often to top up
Make sure it is a valid high pressure stirrup pump (usually sold for PCP air Rifles) and avoid saving some money on dodgy imports
Ensure it is suitably filtered, noting that any contamination will at best clog up the regulator and result in a burst disk failure one day, and at worst cause a flash fill explosion once filled at a later date when filled by compressor and heat gets involved
6) by compressor. Domestic and workshop compressors are no good as they can’t reach the pressure required - and cause contamination
Your would need to spend thousands on a diving compressor
7) with a ‘shoe box’ booster compressor
couple one of these to a workshop compresser and it boosts the pressure.
It will still take ££s, is very slow (taking days to fill) and the source compressor will keep stopping from overheating