Note - it will be preferable to use HPAC or arrangements through paintball sites & retailers
However only IDEST centres can hydro test, and will know about paintball cylinders
(Of course HPAC are an IDEST centre)
Any dive centre may also offer testing, but unless they are on the list they cannot test but arrange the test with one of the centres
Dive centres can be useful as a local drop off/pick up point, but may or may not be paintball friendly
I once had a cylinder tested via a local dive shop, for a good price. I later enquired about retesting other cylinders and had a major quote. Either the guy I spoke to did not understand the question, or more likely did not want the business