I'm a SodaStream addict with the objective of cutting down the cost of my monthly buzz. I spent about a month trying to track down the proper connections for a C02 tank/refill.
Here ya go,
Recharge Center in Calgary - google it. Blackfoot and 58th Ave S.E. $25 for a 10lb Co2 fill. $160 for a 10lb tank + fill (not always available) . $5 for testing. Everywhere else I tried either refused to do it or cost was $50 and a week's time.
I bought a tank from them because the one that I had shipped from Kegworks had cracks in the threading (computerized testing done by Recharge Center). Kegworks has offered to ship me a new tank, so I might have an extra one soon.
Soda Stream filler kit - sodac02.com - This will let you fill the sodastream bottles from a large C02 Tank. Beware - I've heard some negative things on the seller - but I took the chance and it seems to work fine, other than a pipe fitting that needed some more Teflon tape to seal it. I think each kit he sells is individually made so there's a chance some of his kits may not work 100%.
BE SURE to either get a siphon style large CO2 tank (so that it draws liquid CO2 from bottle rather than the has at the top, or mount large tank upside down to dispense. I think you can get a siphon installed into an empty tank?
Finally, if you need a sodastream tank filled, either exchange it for a full one for $20 + tax at Bed Bath and Beyond, or get in touch with me, N.E. Calgary near Deerfoot and 16th Ave N.E. - I'll swap it for $15 including tax. cbantli (at) gmail.com.
Anyways, I realize that doesn't completely relate to your post, but it would have been nice If I had that info here before scouring everywhere to look for it.