Lots of small specialist shops around on highways. I normally buy from Robinson Handyman in the Mall though. Large sacks of dried food their are good value.
The Agrivet stores, feed stores, that are everywhere sell it. The grocery stores and Handyman sell it. You will get the most value at the agrivet but you need to know the nutritional values on what you want. It's best to look at the bag for the info to save confusion. I go to Pacific Agrivet. It is around the corner from the Mercury drug that is across from the market in downtown Dumaguete. I think they are reputable. They have a few puppy and regular foods. Be sure to check the nutritional values on the bag they get it from so you can get what you want. That Pacific agrivet gives you the same food as the bag they show you. No switching products. All the feed stores I have dealt with sell by kilo or even half kilo. Grocery and hardware stores by the bag.