Have you considered buying the 2009 ADA practice test? I realize you're asking for source(s) that are specific to RC and give a decent amount of tests to practice for, but consider that the above test provides passages that had been in use on the actual exam, would be a good frame of reference for what to expect and for evaluating other test prep materials.
Personally I've just practiced through practice tests, which adds up to essentially 8 RC tests.