I really think anywhere you'd buy meat would be ok. I don't think the dogs need anything more special. The key is to buy it in bulk to save money. You might be able to get deals from a local butcher if they have certain cuts that are cheap or undesirable to sell to people...? Idk, i'm still learning myself. Someone else could help more.
My dog is very old and most likely getting put down pretty soon. I, and my family, are 100% dog lovers so im sure that we'll be looking for a puppy pretty soon after Mystic goes. I've already been researching raw diets because that's definitely the direction i'd like to go with this dog. Between seeing Coleslaw's, Satomi's and Pookie's dogs i was 100% convinced.