Actually, I think Walmart might do pet portraits. I used this site:
Pet Portrait Studios in ... and put in my zip code. The first one to come up was Walmart Portrait Studios. Not sur ehow much experience they will have working with pets though.
I think you would have better luck with a private photographer that either specializes in pets or at least has experience working with them. Might cost more but results should be worth it. Another place to check are the dog clubs in your area. They will probably have some photographers to refer.