Dave, have you tried GroundUp Restorations yet? They seem to carry some really obscure stuff that no one else will. Such as the plastic piece that goes under the dash by the steering column that I've been searching everywhere for. They don't have much listed on their web page but they do offer a free catalog if you mention you saw the add online. I just ordered my copy so I am not sure if they carry it, but they would probably be your best bet.
Being made of stainless steel these pieces don't rust out. They just get chewed up by wiper arms and blades dragging on them. There is a wide strip for the hide-away wipers and a narrow one for the non-hide-away ones. You'll have to find a good used one, which shouldn't be too hard.
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