One thing i thought of, do you have any gun shops near to you, as they can usually fill markers and have there system setup to fill direct to the fill nipple.
The air systems they have for guns are the same for paintball. My local gun shop can charge up to 3000psi and does this regularly for airguns. As soon as you show them the paintball marker they are happy to charge them for the same cost. Try and speak to the owner of the shop as most assistants don't even bother to help.
Well there's a coincidence, I think Bales in Richmond Road do, Litts in Newport definately do, and Keen guns in Bridgend do aswell.
Where in Cardiff are you, i'm in the back of Pentwyn.
Just checked with bales, and yes they do charge air systems, the guy to speak to is Martin. He's out for about half an hour so i will ring back later and find out the details regarding pressure.
Going back to scuba centers Bristol Channel Diving, by the magic roundabout fill up to 4500psi, but i use Remar in Caerphilly, they are far more helpfull.