some sites will do refills for you, and alot of the time when you go to play they provide you with a bottle full anyways since co2 is normally included in the entry fee
little word of warning ..due to some ****s playing silly beggars with theyre markers offsite a lot of sites refuse to fill tanks for you if your not playing on the day and some will go as far as emptying your tank when you leave ...best check with the sites you plan to be using first .
Unless your marker won't use it you may be btter off going for a cheap air system. There are a couple of places who will do a 0.8 aluminium bottle (300psi) and a preset reg for £40-£60
Bit more expensive than a 20oz co2 but a hell of a lot easier to get a fill of air than of co2
I just did a quick check and your spyer pilot ACS would run on air (and at the quoted up to 20bps you might find your Co2 freezes up)
Just add to that question of where in MK you are as I'm in the land of glass, concrete and roundabouts too.
Cool, I've made some enquiries about playing at that site a while ago with my old automag on a day oragnised by some guys at work, it all fell through in the end but useful to know where sites are around me.