There's really only one way to answer that, and that's to take some really good quality pictures of a wide sample size of different styles and colours you've used in your work. Then post it around and see if people are looking for your services, or send them in to some painting studios that hire commission based painters.
Don't forget to show off your personal style as much as you can, since sometimes that's a major selling point. I know the only person I ever considered getting a commission from on
MtG cards had an amazingly unique style that I can see many people not liking.
Examples of what I mean by unique when I refer to that artist:
Edit: Oh, and posting other general info is good too, things like how long each project took you to complete and such.