You will struggle with revision guides for all exam boards for Computing, as it's one of those subjects only a few people do.
I do WJEC, and there's a good website for that Called: TheTeacher99, if you google it I'm sure you will find it. I haven't looked at the OCR syllabus, but i think it will near enough be the same to WJEC
Check your college library, they will have books relating to the course there.