Our excellent butcher actually sells 'pet quality' scraps frozen into tubes. You ask and he'll tell you what that batch has 'mostly' in it. He does sell beef only, and chicken only, but you can get it mixed. It's almost always the offal that we humans are too picky to eat nowadays. It's dated, and marked, just like any other frozen meat.
On the other hand, my son volunteers for our local food bank doing pick up from the local stores. They DO turn over three or so days left meat to the food banks. He picked up a full tote of Jimmy Dean breakfast sausage one day last week, and then was shocked when he was shopping with me when he saw that the packages were $4 a pound. Anyhow, stores get rid of meat before the pull date, so they don't have to waste it out as a loss. A donation to the food bank can be written off of their taxes, and goes to a good cause.
And finally, Foster Farms pays return to processing on all their meat that does not sell before the pull date, at least they did this in the 90s. I know this because my father retired from there
. It's weird when my sister and I 'talk chicken' around him. He DID work on the refrigerated trucks, so not like the battery trucks or in processing, but sometimes it's awkward.
Good luck. If you find a good source, share!