Check your local small business pet shops. A couple of good food brand for dogs with food allergies are expensive but very good.
I would start off just with the small to medium bags to see if you dog has any reaction to any of the Brands.
My personal favorite for dogs/cats with food allergies is Prairie. It's great for all stages of life, works from the inside out, and if the dog is over weight it will bring them to their ideal weight and visa versa. I have used Prairie many times for my parents dog and cats and my own cats. It's one I will swear by and die by. It is pricy, but so worth the money because of the condition of your companion gets better and better over time.
If you follow the feeding guide lines you will notice your dog won't poop so much or as often, your dogs coat will start to get shiny and healthy looking, and the teeth will start to also look better. Prairie also has canned food and all natural foods such as raw meat. It is safe to give it to your dog once your dog is used to the food.
So your best bet is go to local small time pet shops (most of the best brands of dog/cat food for dogs/cats with allergies only sell to small business pet shops), look at the back of the bags and ask around. Start with only small to medium bags to make sure the food is agreeing with your dog and if your dog likes the food as well.
Good luck, and hope you find the brand that you and your companion enjoys.
Annie The Pet Nanny