For locating a book or journal in the nearestlibrary, the most performant resourceis the Karlsruhe Virtual Catalogue, withworldwideresearch incl. Academiclibraries as well as bookshops (if desired).
For findingelectronic versions of recentpaperspublished on major journals, the easiestwayis, of course, to go to an academiclibrarythat has IP access to the major online article databases (i.e. Jstor, Springerlink, Brillonline, etc.).
For anykind of article (from the oldest to the newest), a very good and efficient (but alsoveryexpensive) quick copy service (printed as well as electronic versions) isprovided by the German, Swiss and Austrianresearchlibrariesthrough the Subito website.
For buying out-of-print books, weadvise to browse first the AddAllwebsite (used section) : it compares the pricesavailable on all the major antique books networks (Zvab, Abebooks, etc.)