[Lynx enhanced] DD-B

Try the Used Market

Like all books ever published, The Phantom Tollbooth by Norton Juster should be available on the used market. If you're lucky, it hasn't become a collector's item (with the corresponding price inflation).

There are a number of useful sources for used books on the net, including:

Bookfinder Search Bookfinder, a meta-searcher for used books
Advanced Book Exchange

Search for book
Amazon.com Search for author