thanks for the tip! i have a mate who has a costco card so i'll ask him if he can look for some for me!
on another note, the biggest downfall with the sodastream is the cost of replacement gas cylinders. i'm working on an adapter that will make it so i can fill sodastream bottles from regular co2 bottles (and save a FORTUNE on extorsionate gas refill prices). the biggest problem i have is the new thread on the sodastream bottle, 4.4mm pitch trapezoidal! the bottles also use a special type of pin valve instead of a conventional on/off type. the main problem as i said is the thread, a thread cutting tool to cut this thread is being a pain to find, i made have to try and make something myself to cut this thread. if i can get that done i can just hook it up to some hydraulic hose then at the end of that i can put on a standard co2 nut (bs341 no.8 thread) then fill from large co2 cylinders for about £1 per fill of the larger bottle
by the way for all interested the '60l' sodastream co2 bottle holds 500g of co2.