Some ways to get copies of a dissertation or masters' thesis include: (a) calling the library of the school where it was submitted; (b) searching for dissertations in the Proquest Dissertations & Theses (PQDT) database (available through many sources including Dissertation Express; subscribers click here); and/or (c) contacting the author (if necessary, see "Finding People").
You can search for dissertations on a particular topic or by a particular person using the ProQuest Dissertations & Theses Professional database on ProQuest Dialog.