i worked at walmart for three years and i'm telling you it's gonna take more than one person in one state/ store to get their attention, as i'm sure you've gathered. Walmart is the devil. They push single people's concerned under the rug and do anything to keep you quiet. If you all decide to go after walmart, it's gonna take a HUGE effort. Now the PetsMarts and Petcos of the universe are a little easier to go after since they haven't reached the mammoth size of walmart. They deal in millions, while walmart is billions.
I do find it promising (in some sense of the word) that you recieved an email, even though it was mostly a form email. Keep it up and hopefully something good comes from it.