I mean, we live in a time when 3d printed guns exist, I’m pretty sure having a 3d printer and ordering filament is probably about as likely to get you on a list as ordering some whistles
But whistles are readily available and cheap, without looking too hard I can get a dozen from them at target for less than $5 with lanyards. Leave your phone at home, pay cash, take a bus or park in the next shopping center over or wear a mask like you’re getting over a cold and a baseball cap and you’re about as anonymous as you can get.
Can probably get them even cheaper if you shop around a bit, if you have a party store around you I’ll bet you can get a bunch there for cheap as party favors for a children’s birthday party goody bag or whatever.






I’m sure it’s more complex than I’m making it out to be, but each gas in the air has its own freezing/melting boiling/condensation/sublimation points, so I’d imagine you could just kind of take advantage of that
Basically just cool it down to x temperature at y pressure, and all of the carbon dioxide should be solid, the oxygen a liquid and the nitrogen still a gas, and they’ve all sort of separated themselves out. Fish out the dry ice, siphon off the oxygen, and you’re left with nitrogen.
Might need to do a couple more rounds of that on each of those to account for other gases in the mix depending on how pure you need it to be, but in theory I imagine it could be that simple (again in practice I’m sure there’s probably a lot of details I’m missing)