When you switch a dog food back and forth, it will cause some upset. Any food change should be done gradually, over the course of at least a week to 10 days. It normally takes at least a few months to get a true picture of how a dog will do on a new food.
The vet tech doesn't have any nutritional training, she only knows what the big dog food rep's tell her or what her boss tells her (which is likely the same thing). Most vets do not have any nutritional training outside of the basic course required to get their degree, and these courses are most often taught by representatives from Hill's & Medi-cal.
Although you may not be able to purchase Orijen or Acana locally, you can order it online. I live in a rural area and the only pet store that carries decent food also sells puppies, so I don't shop there. I order both my kibble and my canned food online. It takes a bit more planning to make sure I don't run out - but it's worth it. There are lots of places that offer free shipping over a certain dollar amount.
You said in an earlier post that you didn't want to start taking things away but rather wanted to find a food that would calm his stomach first. Sometimes, the only way to identify allergies or intolerances (without doing allergy testing at the vets) is to do an elimination diet. You can also compare the ingredient listing of each food you've tried and make a list of the ingredients that are present in all of the brands - then look for a food that doesn't have those ingredients. However, if you switch your dogs food every 2 weeks, he will continue to have digestion/stomach issues. You need to pick a food, and stick with it for a little while. Not to say that if your dog experiences explosive diarrhea with a food that you should continue to give it to him, but just to give the food a chance.
Livin in a Newfie Drool Zone