Use Duracoat from Laur Custom Weaponry. It's a firearm finish and comes in a bazillion colors and I regularly spray it out of a cheap $20 airbrush. If you don't bake it in an oven it will take two weeks to completely cure but you can handle it within 24 hours. In fact, I've sprayed a gun before and shot it the next day with zero ill-effects. I've used it on several firearms and plan to soon use it on my bike. Sand down to bare metal if you can but in my experience just a decent sanding will suffice. It's super tough and scratch resistant.