There's another option which I used on my fretless project - acrylic lacquer. Most car paint is that type, so you can buy primers and other materials at a car parts store. Also, most touch-up paint (and boy, is there a wide variety of colors) is acrylic lacquer, so it's easy to buy in rattle cans. Stew-Mac also sells acrylic lacquer in various size containers, and their dyes mix with it nicely. A car shop could easily work with acrylic lacquer.
Does anyone know of a reason to choose nitrocellulose lacquer rather than acrylic lacquer? It sure worked nicely for me.