this is the second 280E this guy is parting, maybe he has more coming?
8/77 W123 EURO 280E RARE M110 DOHC eng. Parting or Whole VGC Black Int. AZ Title - Benzworld.org - Mercedes-Benz Discussion Forum
don't see the manifolds in the pic but doesn't mean they're not there somewhere. last one he parted/sold had the ones you were looking for. unfortunately, most of the ones you'll find have had the egr plumbed into the front-most one. here's his last part out, but unfortunately the manifolds went with the car:
1980 W123 EURO 280e Parting or Whole GOOD AZ TITLE - Benzworld.org - Mercedes-Benz Discussion Forum. no egr either, i almost bought them myself.