There is a site that is very useful for locating a specific book within a series. It really comes in handy whenever a patron asks for a certain volume in a series, how many books in a series, etc.. You can search under series title, series subject, book title, or book author. It is:
http://www.mymcpl.org/books-movies-music/juvenile-series
I saved it under favorites as Juvenile Series and Sequels.