Hi Dave - I have some armrests and mounting hardware on Ebay. It is of a different style than the ones you have pictured -- I'm not sure how it mounts. The armrests are the same with the two studs sticking out, but the way it mounts to the seat is entirely different. You might want to look at the pics in this link (mine) and buy it quick if you want it since I have an offer already that I'll probably accept in the next 24 hours...
Mercedes Center Arm Rests black W108 W111 280s 280 se sel 230 220 one is broken | eBay
It's worth it for the parts easily, if they are the parts that you need. Which I don't know.

My ebay listing also shows how the parts go together. I think that the part that mounts to the seat is different, but that the armrests themselves are the same

Scott