Date registered: Jan 2013
Vehicle: 90 350SDL, 98 S420, 97 SL500, 94 S420, past owner of W108/W112/W114/W123/W124/W126/W140 & W220 cars
Location: Tampa, FL
Mentioned: 8 Post(s)
Quoted: 604 Post(s)
You would be looking for a "Universal", which is a coach built fintail wagon made by either Binz or IMG, I believe.
Both of these were cars with body modifications made outside the factory, meaning that in many cases parts are rare if not impossible to find, especially body and trim.
There was one that just popped up recently in the "Vintage" conference - you might want to look over there.
Otherwise, I would look at places like Hemmings where you are more likely to see vintage and one-off vehicles.
Good luck with the hunt,