You could buy your own portable diving compressor, my dive buddy has one, there not silly expensive .
You must get fills from a compressor designed for diving (breathing) as the air is filtered and moisture removed.
Used Scuba tanks can be found on eBay, but for new equipment, there are brick and mortar "dive shops" that sell tanks and other diving accoutrements. Scuba tanks can be found online at Amazon, and at other online portals that specialize in diving equipment such as LeisurePro.
SCUBA tanks are metal (usually steel or aluminum) that are filled with compressed air. This is loosely related to a pneumatic system.
Hide behind those water tanks. The scuba tanks are filled and ready to go.
you buy new ones not refill them
They have underground tanks refilled regularly bu tankers.
Most SCUBA divers dive with compressed air, which is normal atmospheric air compressed into a scuba tank.
Yes, in-fact only pin valve tanks are refillable. Ones with a non resealable top can't be refilled.
so the diver can breath.
By oxygen tanks - similar to SCUBA divers.