We get our pet portraits done when PetClix (
Welcome to Petclix - The Pet Portrait People ) roll through town every year.
Once a year also in Jacksonville they have a Pet Expo which has numerous pet photographers who set up booths advertising their service. Maybe your town has something like this as well?
Also, I know whenever I go to a pet bakery around town they all seem to have bulletin boards with pet photographer's cards on them. I'd check around your town. Maybe even your yellow pages would have pet photographers listed.