Hi Jeffry,
I came across your the comments on the availability of the book(s) on you blog and though I would explain. The books were only to be published as a two volume set, but eventually it was decided to make them available separately. So, there was one set of ISBN numbers for the two volume set, which was then pulled, followed by a new set of ISBN numbers for the individual books.

If you really want you can get them through Amazon. All of the ISBN numbers and the links to Amazon are on the web site:

http://www.chris-kimble.com/CLEE/ToC.html

Bizarrely, in the UK, two two books bought separately cost less than the two volumes bought as a set!