Secrets is still in print, I’m happy to report, but only in the form of a multi-user ebook. If you’re interested in purchasing copies of any (or all) of the five titles: Objects in Motion, Matter and Energy, Liquids and Gases, Waves, and Relativity and Quantum Mechanics, please visit the Lerner Publications website
You can still find some of my other books at Lerner as well.
I also have a few print copies available for sale. Please email me for details.