I picked up a gorgeous seltzer water bottle at a yard sale-it is heavy glass, with a metal mesh covering. It is perfect except that I am missing the CO2 screw-on attachment-which allows you to charge the water with the CO2 gas. I went to a home store, and they had no replacement for this. Is this something I could make? It is basically a threaded cylinder that you insert the CO2 bottle into, then screw it on to the bottle.
Find someone that sells C02. Hydro shop will have your fittings if there’s no other source.
Google soda siphons- maybe a spare from modern day commercial ones will fit?
Try eBay.