Local butcher shops. But they don’t have storage that I have ever heard of.
I have never heard the words “locker” and “plant” used together before.
It never occurred to me that they weren’t everywhere, although I’ve never had any reason to go to one except in Texas. There was one on the main highway not far from the ranch-the unlucky cattle and hogs were taken there to be turned into cuts of meat and wrapped for the freezer.