I have some experience with this, having both hired voice talent and occasionally doing voice work myself. One route is to find a professional recording studio and talk to the owner or one of the engineers. Sometimes they have classes or know where you can take classes, and this is a good way to network as well as polish your craft. You might even get some work from a studio.

Another route is to find a talent agency and audition.

In preparation for either of these routes, I suggest you do some personal recordings and make a CD