i have a 232 bar dive tank, obtained from a dive shop in fenny stratford milton keynes. the place is worth a look as you pay upfront for about 15 air fills and the tank is free....it works out about the same price as a dive tank from other places but has the advantage of not needing to pay for fills the first few times...
i usually get about 4-6 fills in the 4000psi range and then it drops off giving about another 6-8 in and around the 3000psi range...then lower and lower.