What materials have you been using so far (books, courses, online materials, etc.) during your studies? And are you just interested in RC or are you looking for a complete set of materials?
Next, if you are looking for retired official GMAT passages you can use the Official Guide to the GMAT 13th edition or the Verbal Review 2nd edition. Or you can download the free GMATPrep software and the add-on the "Prep Pack 1."