I have a book called Celtic Illusions. It also teaches you how to make your own designs as well.
It's a great book if you are able to find it for a good price
http://www.amazon.com/Celtic-Pieced-.../dp/1574329162
Maybe your library can get a copy of it? Mine is able to get books from local libraries as well as others from around the country for about $3 or $4.