When Passage to India is entered as title in UD's Online Library Catalog there are at least four books which may be helpful for criticism of Forster's work.
In the Databases try JSTOR with title, Forster, criticism=375 results. Then repeat with Project Muse=one result. With Humanities International Complete there are 26 results and go to the top of the page, click on choose databases, click of Academic Source Complete, Masterfile Search Premier, and MLA=86 results. Literary Resouce Enter = 4 results. Literary Criticism = 1 result (begin on p. 176). In WorldCat there are at least 4 dissertations about Forster and Passage to India. These should provide the sources needed for your research.
