Interesting. Never heard of silk screening on walls but why not? If there is that much profit to be had buy some supplies and figure it out
Fastest way to screen print something is to cut 4mil vinyl and apply to a washed screen.
Saves all the work of "burning" films, working with emulsion etc...
I know as this is what I used to do. Got out of it when I was tired of the clean up and dealing with another waste stream.
Wouldn't take much to build and paint a practice wall.