I've probably mentioned this, but it's been a while. Too, the number may have increased since then.
These all appear to be backlist books (nothing in the world wrong with that)--books that are all very good quality, but The Met no longer sells in their gift shop, for example.
Navigate to
this The Met webpage to find all of them, from 1964 forward.
Don't forget that The Getty (Museum) also offers a boatload of similar ebooks for free.
Thank you, The Metropolitan Museum of Art!