In general, you should not be able to find the most recent paper for most GCSE exams. They are generally held back until later in the academic year. I you have not done used them already, the other past papers for the syllabus (available at http://www.ocr.org.uk/qualifications/gcse-gateway-science-suite-physics-b-j265-from-2012/) are generally just as useful, as the syllabus did not drastically change from 2012 to 2015. If you want the most recent paper, you will probably have to wait until some time into the new calendar year.