I'm sure if you gave Martin or Caroline a ring at Anglesey Divers (Holyhead) they would try their upmost to fill your cylinders if you require them being filled out of shop hours - their service and customer care is beyond expectations usually.
Give them a call anyway
01407 764545
http://www.diveanglesey.co.uk/dnn/ info@diveanglesey.co.uk
Otherwise it's Pembrokeshire or Chester area I'm affraid!
Irfon