I found this on the Animal Ark's Shelter page. It documents puppy mills in Minnesota. During the video, there is a short scene on puppies sold in what looks to be a Petland store, a chain notorious for acquiring all of their puppies from puppy mills, although they vehemently deny it. Please be warned, as this video contains graphic content, particularly toward the end.
http://www.animalarkshelter.org/
http://www.animalarkshelter.org/