Hi Jacob-
Grain free is inconsequencial to the proper growth of the dog, which is the ultimate and most important goal that should be focused on. Grain free also is not inherently better for allergies (especially ones that may or may not manifest themselves). I would focus more on finding a food that will help your dog grow properly and less on marketing gimmicks. However, if you are 100% positive that you need to feed grain free Nulo Puppy is a grain free food formulated by a veterinary nutritionist, that is safe for large and giant breed puppies.
As far as what is available to you at PetSmart, the only brands I would recommend from there is Pro Plan Large Breed Puppy, Science Diet Large Breed Puppy, Royal Canin Maxi Puppy and Eukanuba Large Breed Puppy. The other brands I would recommend you would have to purchase online or at a speciality pet store.
