In my state, pet stores are considered essential businesses, so I can buy my dog's food at his usual place. This particular store is not allowing any customers inside. I call ahead, place my order and pay via credit card, and they bring it out to my car. They also have a walk-up station outside.
Moreover, you can buy dog food at grocery stores, places like Target, or many home improvement stores (like Menards here) that are considered essential and open. Ideally, if you are going out to buy your own food at a grocery store, you should have no problem buying dog food as well.
If your grocery store (Hannaford) doesn't do deliveries itself, some groceries have curbside pickup or you can do something like Instacart. There are many, many options.