The United Nations released its World Digital Library: an open digital library collecting materials from several different countries, in different languages and from different time periods.
This was a project proposed to the UN by James Billington, director of the US Library of Congress. It provides nowadays access to the libraries of 32 institutions. The UN has as a goal to expand the number of institutions that are part of this project.
There are different types of materials available: books, journals, manuscripts, maps, motion pictures, prints and photographs, and sound recordings. As far as I could sense, the majority of this material is from the period before the XIXth century. The items prints and photographs, motion pictures and sound recordings are probably the ones containing most of the material from the last century. I couldn’t find anything related even to famous economists (Quesnay, Smith, Ricardo, Marx, Keynes, etc). Nonetheless, as the UN promises to expand the project, this may become a more relevant source for the majority of the historians of economics.