A good way to find a store or boutique that carries the good foods is to use the "store locator" on some of the premium food brand websites. Generally stores will carry more than one good brand.
Merrick Pet Foods : merrickpetcare.com The Healthiest Pet Foods in the World – Natural & Organic Pet Food – Natura Pet Products Nature's Variety
Start with those and when you find a store that carries them they can help you decide what food will work for you, give you samples, etc. The "good" brands only sell to independent stores who are more likely to be knowledgeable enough to help you.