I am not sure if this is the right forum, but I figured that people with relevant knowledge would be here.
Is it possible to use CO2 cartridges which were designed for say paintball guns or other things rather than the ones specifically for soda siphons? Essentially, the cartridges are the exact same. If it's just CO2, then it's just CO2. The metal never actually touches the water. The CO2 cartridges seem to be 8 grams of CO2, while most painball cartridges seem to have 12 grams or even 16 grams.
I say this because I have a much easier time finding a paintball/airsoft place than a place that sells the soda siphon ones, not to mention the reduced price.