Just Paintball don’t handle the actual testing, they arrange it. Other paintball retailers can normally do the same
HPAC are the ‘paintball experts’ for all air services including hydro testing.
If you can get to an event they are attending then you can hand it to them in person for collection at a later event - and therefore only pay the cost of the test with no postage involved
Alternatively check out the IDEST members register which lists approved hydro test centres.
(HPAC are on the list under A for Armourlite)
It’s most likely that there is a dive centre in your area that if listed can do the test, or if not tested can act as the middle man.