Go to deviant art, find someone who's manga style you really like, ask them if they can commision you (draw what you want for a price), and send them a picture. That's the easiest way to get someone to draw something for you, and you'll have their gallery to look at to see just how good they are. If you're asking someone you don't know from the internet, there's probably no way you'll get it done for free. Artists are busy people. i know, cuz I'm one of them.
