I’ve read about ballers who pop the top and drop the appropriate weight of dry ice in. There are tutorials out there but it’s scarier than I’m willing to take on.
Me too, but I got a sodamod for mine and refills are $5 at the local homebrew shop. Paintball places are cheap too, or some Dick's Sporting Goods can do it.
There are offbrands like Indigo, but they can be refilled as well. Stores won't do it, but you can buy a 5~10lbs tank from a beer supply store and fittings and adapters from eBay/Ali.
Idk about other countries but there's like several generic supermarket alternatives to sodastream in all bigger shops here, and idk who the fuck would buy the overpriced sodastream brand co2 when most markets sell a generic brand bottle for half the price.
So at least here it doesn't have a majority of the market. Perhaps the largest share, but I don't think the majority.