Hello Alberto. For flowe4 illustrations in color from the 17th and 18th centuries I have found the library at the University of California, Berkeley, useful, also, the Library of the United States Department of Agriculture (special collections section), the Bibliotheque Nationale (France) and the Library of Congress (United States)to be most usful The last two are on line, as far as I know and can be picked up by your browser, the other two, probably. The University of California has a number of full folio size hand-colored orchid books , e.g., Bateman, and the one out of Buitenzorg which I can't remember the name of.