I search the web on sights like Deviant Art or use HeroMachine.
I can also request Character Art on the site I play on in a thread dedicated for such. A lot of dedicated artist there with talent.
And you could always commission art from a artist, though there will usually be fees attached.
Or you could be ghetto and open up Photoshop, pull apart things from other images, paste together in a reasonable/semi-reasonable fashion, and create Character Art from that.
I find myself making characters based on pictures I see rather then making them and then attempting to procure a picture similar in likeness, so I usually don't need to find a picture for my characters.