Emmet Otter Book Info Here!
I have the book, it's tough to come by these days. I worked a Borders Books for four years and did a little research while I was there on this book and that's how I eventually got a copy. It's the only one with Emmet, there aren't any others. The author, Russell Hoban and artist Lillian Hoban have done many other books including the fantastic A Mouse and His Child, and the series Frances, which I believe is something Henson Company is working on bringing to TV. The show is a very close adaption of the book.
To find the book try your local booksore, or Amazon.
The ISBN is 0-89966-861-4, it's only available in Library Binding and might cost around $30.00, but well worth it!