I feed Stella and Chewy's raw frozen and freeze dried along with Instinct canned. You can find it all on Chewy.com My dog has a lot of allergies so these diets are low in carbohydrates and grain-free.
Agreed---there are so many grain-free brands available. Raw frozen, freeze dried and canned have worked best for my dogs.There is a TON of grain-free foods out there. They aren't in just specialty stores, either. You can get grains-free foods at your local supermarket. If you want something else, I know my local grocery stores carry brands like I and Love and You, Castor & Pollux, and Purina Beyond. If you go to a pet supply store like Petsmart or Petco, there is an even wider selection. Shopping online, through places like Chewy.com gives you even more options.
If he liked the Nutrish and did well on it, why not just switch to one of the Zero Grain formulas?
You said he "recently" developed an allergy to corn? How recent? And are you sure it's corn he's allergic to, and not something in the environment, like pollen or grasses? True food allergies aren't very common in dogs. Has he been allergy tested? If so, what type of testing did you do? The blood and saliva tests aren't always that accurate, so the standard for determining allergies and/or sensitivities is still a strict elimination diet.