Here are some of the books that I have found useful. Some of these books are still available new. A source that I have used often, is Ebay. All of the old editions of "Model Engineer", in which the construction articles of both the Simplex and Super Simplex appear in, are available on Ebay.
This is a particularly good book if you are building a Simplex, as this book was written by the designer of the Super Simplex. All the techniques described in this book can specifically be applied.
This book is avail able in hard cover or as a digital down load. It is a good general construction book. I have the digital version. Some of the drawings are so poorly done that text and dimensions are not readable. There is also missing text on some pages.
As the title suggest, this is about the operation and maintenance of miniature locomotives. Fun reading.
This is a very general construction book. It mostly applies to the larger scales, but, does have useful information.
Someday, I hope to make an injector or two. This is the book for sure. It tells you everything you need to know. Very good book.
This book describes many useful techniques especially for the beginner. It also has well written chapter on silver soldering.
This is also a good general construction book on miniature locomotives.
This book is just a republication of the articles that appeared in "Model Engineer." This is a hard to find book at a reasonable price. It is probably less to collect the ME magazines with the articles.
This is a republication of articles written by LBSC. It includes drawings for a nice little steam operated feed water pump.