I use airbrushes daily at work, I have several of them. But for bows, I like a larger pattern than they can spray. I use a touch up automotive spray gun. There is more waste, but I can get a better finish, which is what I care about.
Air brushes put out a small pattern, even if adjusted wide open. You'll get the finish drying on parts of the bow while other parts are wet. The result is an inconsistant shine.
I really like Fullerplast. Expensive, but fills grain like nothing else I have used.
Dan