Re: Its not just dive computers
'although good luck getting a fill on out-of-test cylinders'
Search fleabay, Alibaba etc for dive compressors, consider also the fact that other organisations have suitable compressors required to refill their SCBA tanks..so unfortunately it isn't as hard as you think.
Not a diver myself, but know a number of them from the local clubs, and from them I've been hearing that there's allegedly a lot of 'sketchy' shellfish related diving going on, with training, legality and certification not being high on the priorities of the characters getting rich out of it (needless to say, they're not the ones doing the diving with the OOT gear...).