Bench seat mount, replacement part

My new '74 Duster has rust everywhere, but one of the first things that needs to be fixed is the bracket that supports the bench seat. I can't find this part, and I'm not sure what it's called. Here's a picture, looking back along the driver's side. You can see how the bracket is rusted and sagging, obviously not safely holding the seat in place.

What is this part called, and where could I find one?