I don’t have pics but mine is really simple- it’s a big red extinguisher, I unscrewed the pressure valve on it, drilled it out and fitted a tubeless valve into it (this was a fiddle but not difficult- I did a wee bit of prettyfying in a lathe but it’s not necessary, hand drill and probably a knife and sandpaper is all you need). That all make it refillable.
And I chopped the end off the hose, and found a compressed air fitting the right size to squeeze into that, then attached a topeak valve off a floor pump to that. TBH this needed a little thought but nothing too clever, just assembly stuff.
And that’s it. Mine is a 27 litre, which is fairly ridiculous, it’s bulky and it takes a long long time to charge it up with a pump. I keep thinking I should do a smaller one for the car. But it’ll inflate a lot of tyres once filled. I obviously don’t usually discharge it fully (once it’s up to 50 or 60 it’s useful, and you can just recharge it by a few psi every time; once it’s empty it’s useless and you need to reinflate it all the way back up to 50 or 60)
Cost a few quid. The airshot’s a nice bit of kit but mine has a better valve and is ALL POWERFUL.
(aside; I had a 3 litre coke bottle inflator, didn’t get on with it at all, no better than a good pump imo)