[Leica] Documenting used prices for insurance

[pklein at threshinc.com (Peter Klein)]

My camera gear is covered under my homeowner's insurance policy. But any
single item over a certain value must be declared on a separate rider. My
camera is already insured. But at this point its replacement cost is half
the new price. And I have two lenses that need to be put on the rider due
to "Leica inflation."  All are discontinued models, so I can't just go to
B&H for a price.

Having dutifully checked recent classifieds and the auction site's
completed listings and gotten a reasonable average for the items in
question, I talked to an agent.  She said that they would prefer a listing
in some kind of "trade publication," but in lieu of that, an e$Bay listing
might do.

Is there somewhere I can go to get a value they will accept, kind of like
the "blue book" for cars.  How have you folks documented your stuff's
value for insurance?

Thanks!
--Peter