A minisite dedicated to the book is still live on Apple's servers, but links to buy the book from Apple's online U.S. store have become dead ends. A search for the book on the online store and the Apple Store app also return no results.
Stocks of the hardback book have been fluctuating since around June, suggesting Apple has been reducing print numbers for some weeks. In some other countries, the book is still available through Apple's regional online stores, but stock still appears to be dwindling.
Released in 2016 in two sizes priced at $199 and $299, the publication covers product designs from the iMac in 1998 to the Apple Pencil in 2015, and "also documents the materials and techniques used by Apple’s design team over two decades of innovation." It is dedicated in the memory of former Apple CEO Steve Jobs.
A video starring Jony Ive accompanies the book on Apple's minisite. If that gets removed, the video should still be available on YouTube.