Because stores sell small dogs and the fact shelters and rescues are full of bigger dogs, I don't think pet stores are the problem for shelters. The problem with pet stores is always going to be their supplier. If the supplier can't sell through a pet store then get ready for more brokers. At least with a pet store the SPCA should be able to learn who the supplier is and I'm not sure why they haven't look into that angle. But with brokers they will be hampered as those will be private citizens.