To our knowledge there are no Lassie books currently on the shelves that are authorized or licensed. There are only three books that lassie.net recommends:
1) The Story of Lassie- Told by the master himself, Rudd Weatherwax
2) Lassie, A Dog's Life- by Ace Collins
Who else but the original owner and trainer could tell the story of how Lassie began? "The Story of Lassie" is a treasure but unfortunately out of print.
Our good friend Ace Collins painstakingly researched the history and legacy of Lassie for his book, "Lassie, A Dog's Life- the first 50 years". He spent months working with members of the Weathewax family, cast and crew and searching through archives of press clippings. It is the foremost authority on the legacy of Lassie in existence and has come to be known as the "Lassie Bible". We use it here at lassie.net as our source for the most credible information available. Also out of print, it can be found more easily online.
If you are searching for more information on the collie breed, "The Collie Concept" by Bobbee Roos is the best! Again, this is a highly sought after book that is out of print.