A friend of mine (actually a friend, not me, I have known forever not to buy soda streams I PROMISE I'M NOT A LIB 
) wants to actually try to boycott Israeli products (finally). They have a soda stream though and they want to continue to use it, but they don't want to buy the cartridges from soda stream because they're don't want to support genocide. Since this is a noble goal I want to help them.
So what are their options, where do they buy cartridges for their soda stream that don't support literal genocide. This is their Very Important Treat and they really want their treat and we all deserve our treats so I'm trying to help them. Thank you.
Thanks everyone this was super helpful...looks like you just buy an adapter and then I've got a bunch of local brew stores that will fill the tank!