The reference material on Πλάτων (Plato) is found in several locations: Religious Studies and Philosophy Library (B 351-B 399 non-circulating), Greek and Latin Reading Room (PA 3104, PA 3404-PA 3405, PA 3612, and PA 4279-PA 4333 non-circulating), and Stacks (B 355-B 399 and PA 4279-PA 4333).  Circulating material is found in the Mullen Library stacks. Check the WRLC SearchBox for monographs and journals that could be applicable to your topic.