Great idea on taking a longer ATF dipstick! I've been using the car-parts.com website to track down junkyard e350's...the problem I'm finding is that most of them don't inventory those kind of miscellaneous items. Under part classifications, the best luck I've had is to look up e350 engine blocks or cores and call hoping they'd be helpful enough to take a look.

I'm not really sure what to classify the door buttons under, but I've yet to find any of those in a salvage inventory. (Maybe under electrical? but none found on the search) I'm assuming they just don't bother to inventory those.

My experience with junkyards is that if you call them about a specific vehicle

they can tell you if they have it or not.

If you show up, they may or may not let you look at it.

If they let you look at it, you can get the small parts you need.

Sometimes cash, no receipt.  

Have you tried JC Whitney, Dorman or Partsgeek?  You may be wasting your time using their web catalogs too.  Try calling them.  That's especially true for JC Whitney.