I have been getting my fish and supplies in Spokane and Lewiston.
Spokane has Northwest Seed and Pet on east Sprague. They're a very large store with an extensive fish and aquarium section, and fairly knowledgeable people.
Lewiston has Bob's Pet and Pond. They take extra special care when bagging fish by placing a little blue pill in the bag water which acts as a relaxant to minimize stress on the fish. Customers who have to travel a long distance to return home can count on their fish still being alive and healthy when they get there.
Both are good places.