You can just buy it at the appropriate gas supplier, my local university used to sell it. If your parent was a nerd or a welder it would be fairly easy, it can just be expensive getting an appropriately sized dewar if a thermos isn’t big enough for your usage (or if you can’t find someone willing to sell you only a thermosful, which is admittedly a little dangerous)

My physics department had a spigot coming out the wall and sheet with the number of liters you poured yourself. It was about the price of milk.

This is exactly correct. The nerd/hacker acorn doesn’t fall far from the nerd/hacker tree.

Same reason I had a spare 286 lying around

My university was the only place in my city that had a plant for liquid nitrogen so they supplied all the hospitals. They also were pretty cool about giving it out, so you could do diy ice cream or minor cosmetic procedures.

My dad got it just to play with on a couple of occasions. We froze and reanimated brine shrimp once..blew up a 2 liter bottle (do not attempt - it was really loud). He just got it from a gas supply - I’m sure it’s the same situation today. The liquid nitrogen itself is fairly inexpensive, but you need to rent a special container for it.

Dewar flask is the container. Hospitals also have liquid gasses but don't usually sell it directly.