I went the disposable cannister route, purely because after phoning around everywhere I couldn't find anywhere willing to refill cannisters.
I bought the regulator and 2 bottles from WeldUK on the web for £50ish.
Then the solenoid and needle valve from Lunapet on ebay for £30ish.
Gotta get it reset after trying to run it with a second hand cheapo needle valve, which was a mistake a it turned out useless and discharged 2 whole cannisters into the tank. (The first killing all the inhabitants)
Waiting for 2 new cannisters and away we go on the fine adjusting route again, hopefully not killing the inhabitants this time.
Good Luck with your tank. Looks good, and nice lush growth, but keep an eye on the lighting situation, as you may now find that doing the lighting upgrade before sorting your CO2 out could result in huge undesirable algae outbreaks especially on leaves at the top of the tank with direct light. I hope not and keep us updated.
Andy