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There are always institutions to consider - you'd have to consign to a US seller though with the right connections.

Yep - agree with the above, it might be a good idea to weed out the bits that you like the least and put them on eBay or at an auction house, get rid of duplicates etc. - see how it goes, see if...

Depends how quickly you want the money.

That many items isn't going to do too well at auction I wouldn't think. And you'll be lucky to find a bookseller who'll offer you a decent quote (except...