You can actually do this yourself if you have airbrushing equipment. I've painted a few with good results (did a cool blue sunburst design on one 🙂 ). If not, anyplace that does custom car painting might be able to help you out, but it would still be cheaper to do it yourself.
If you do it yourself, you'll want 7-8 THIN coats, then a couple of clear coats over that to make it look decent.
IMPORTANT EDIT I almost forgot- if your guitar has acrylic paint on it, BE SURE TO WEAR BREATHING FILTERS WHEN YOU SAND IT DOWN!!!! Acrylic paint dust is a awful lung irritant, and your lungs will swell up and be sore if you breathe enough if this stuff in. Thought I'd warn you if you were going to try this yourself.