Well, Mossberg finally got back to me, and the bottom line is that the gun has to be sent back for repair. Following is the email I received from them.
"You are unable to find these parts because these firearms are imported and all the internal components minus the firing pins and springs are...
I'm not sure what you mean by "side plates" It's a box lock action so there are no side plates unless there is some terminology that I do not understand.
OK. Here are some photos. The little spring(?) needs no explanation, it is what it is.
The other photos show the "rocker" blocking the triggers and then pushed back to allow the triggers to fire the gun. A wooden pointer is indicating the "rocker". The other photos show the safety/barrel...
This 12 gauge O/U was brought to me for an unrelated issue to the title which I repaired.
However, there are two problems that I now face.
1. When I removed the stock a "square U" shaped spring(?) fell out and I have no idea where it goes. I have tried to find a decent schematic of these...