Are you sure? Merrick has grain free flavors, but also has some with grain flavors with barley, quinoa, and rice, like this one:
My vet also recommended some of those brands, but my dogs are allergic to chicken from dog foods (they are fine with chicken I make at home, but always get a rash and/or diarrhea with store brands), so I tried the Merrick I linked and haven't had issues.
I used to feed them Acana Pork and Squash.
EDIT: Direct link to ingredients in the Merrick food I linked above: https://images-na.ssl-images-amazon.com/images/I/91Q99OzKdiL._SX679_.jpg