Nobody - they've been discontinued by GM for a long time. There are folks that sell a replacement using a rubber strap and a bolt that you can attach to your broken stock hanger. You can do it yourself, too, with a universal strap-type hanger from the auto parts store.
That's what I'm talking about. You take the 2 pieces left after the rubber part breaks and bolt a new piece of rubber to it. It comes out just like stock except the rubber isn't riveted.