|There are a few places where you can post want lists more or less permanently.
They can be scanned by booksellers, other collectors, or anyone passing by. It's not really the most efficient method, but you never know, and it doesn't cost anything.
in the end all collectors are always looking for the books that should be added to their own collection. I for example am always looking for books from Tolkien's personal library. You can imagine how many email subscriptions I have looking exactly for books like these.
I don't hold the time to go searching for hours and hours so I subscribe for some searches and get all result in a digest as soon as the books do come online. The books I'm looking for are so rare that only by subscription I manage to find new books to add to my collection.
AbeBooks.com has a very nice wanted section where you can exactly say what you would like to have (be precise about title, edition, price you want to pay for it) and once in a while you will get mail when a book matches you wants
Ebay has a similar system, but it will be sending a lot of emails out. Also it is not so handy, because the mails are based on the ebay search system (you get a lot of items in a list, but most of them are not of interest to you).
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