To start with I just ran with a cheapo regulator and some silicon airline - which fed the gas into my filter inlet... but the POP sound as the bubble drove me nuts, so I bought a ladder diffuser off ebay.
Whilst trawling ebay, I found a "needle valve" for next to nothing - this is used to finely adjust the gas flow, but to be honest - with a little patience you can do that with the knob on the regulator.
The gas I buy (1 - thats ONE a year !) is from Machine Mart... they do a high capacity version (010131057)
GAS BOTTLES
Heres a regulator - 010120110
Regulator
ANY welding shop will carry these, so shop around... but dont forget - you need ONLY Co2...
Whilst you are at the shop - beg a short length of reg - welder pipe, you only need 2 inches or so... this fits into the reg, and is a snug fit inside airline !
Good luck - if you need any more help, dont hesitate...