Call the Smithsonian. The slides might well belong in a museum. With respect, it would be a shame to sell the slides to someone who will put them in a collection, or sell them off to other collectors.

You might also call the SF museum of Science, or the Yale University Sterling Library.....the latter has a rare book collection that is stored under perfect conditions. Realizing that you have slides rather than books, perhaps they might still be interested....there are also Berkley and Stanford..