There are many different ways to obtain my books, depending upon the specific title. Whenever possible, I encourage you to patronize independent booksellers. They are the heart and soul of the retail book business, and as long as a book is still in print, they can usually order a title for you if they do not have it. Large chains can also order titles. It's helpful to have the ISBN, which you will find on all my book pages, but you can also order by author and title.
Online booksellers have my in-print titles readily available, so that can be a convenient way to order. I have provided direct links to my books at Amazon.com and Barnes and Noble online.*
For books that are out-of-print or out-of-stock indefinitely, I suggest trying BookFinder.com. This is a wonderful site that simultaneously searches several used books sites.
I have also supplied information for direct orders from certain publishers. National Geographic and Harcourt will both offer generous terms if you place a multiple book order and explain that it is for an author visit. Facts on File books are aimed primarily at the school and library market, and they can be ordered directly even in small quantities.
*The Authors Guild is currently challenging Amazon.com over their practice of offering used copies of a title on the same page that they offer new copies. This cuts into the author's ability to earn royalties, because royalties are only paid upon the original sale of the book. Obviously, Amazon offers a great service to book lovers. However, I do support the Authors Guild's point of view in this matter, and whenever a book is still in print, I urge you to buy new copies. Barnes and Noble does not use this practice.