Search the various forums for them...I have seen not-so-positive reviews on those materials before. I have not personally used them, so I can't say myself, but I did use Princeton Review
's Cracking the GMAT
and would highly recommend it. Their techniques are very effective. I don't think there are any real secrets to the GMAT; it's just a matter of learning how the test is constructed (which is essentially public knowledge through many books at this point), learning how to approach each question type, and practicing your butt off.
You'd do better with the PR book (with the CD) and the Official Guide. Also the Powerprep tests from mba.com.