Rich Muller notes that "many of the pieces that have been in the Huntington's Scott gallery are now up for auction (through Sotheby's). There are a lot of high-resolution images that I've never seen anywhere else. Get your checkbooks out, or at least download some of these images! There is also information on each lot." Catalogs are US$43; the least expensive item up for auction is significantly more expensive.
Of special note, at least to those interested in the graphic arts: some of the most expensive cuts (of such a small size, at least) ever.