Those are fun!
We did one on a small scale at work with leftover/scrap parts. It was smaller than the one you have though.
You need a constant regulated compressed air supply, a constant regulated cold water supply with a misting nozzle, a venturi, and a section of pipe to act as a mixing chamber.
The venturi creates a cyclone of air in the pipe and as the cold water mist is added you create snow. You have to adjust the water and air supply to get it right otherwise it just makes a watery mess.
The one we had at work isn't around anymore so either someone tossed it thinking it was scrap (right back where it was born from
) or someone took it home to play with.