If you still care about idiotic software patents and
stupid "business practices" patents, avoid Amazon and
instead. E.g., http://isbn.nu/1-55591-235-4
gets you to a list of a couple of online used bookstores
that might have the Millers' book.
For PCT books in particular,
I'd recommend Berger's and Ross' books (and reading all
of the archives of the PCT email list and all of the
hiker journals that one can find on the web)
in order to get a bit of a hint of an idea what a PCT trek
can be like for some people who do not happen to be you.