Surely you have a small LR parts place near you or I would have thought Richard @ Beamends could get a courier to get you one quick. These mechanisms are rubbish and even a small LR place should have them in stock. Getting a s/h door seems to be overkill and its window winder would probably be on it's last legs anyway. S/h doors worth about a hundred quid if it's decent enough for your uses, and a new mechanism is less than twenty quid (plus a whole lot cheaper to ship). I know what I'd rather do....
Another thought, if you have a 110 station wagon, what about swapping the mechanisms from the door behind - I can't recall exactly how it goes since I haven't done if for two years or so but it would be worth double checking the regulators to see if they're the same, they are handed, and the channel may well be different but I would have thought that LR would have reused them. Then you can just jam the middle row window up to get you moving, not ideal though if you have kids in the back.
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