There are some books on sailing Mirror dinghies that have been published in the UK over the years.
The books which are no longer in print do turn up in used condition from time to time on sites like Amazon, or in local second hand bookshops. Needless to say, a book written in, say 1980, will reflect the rules and state of Mirror sailing in 1980. Things move on, ideas change, rules change, so the older books will be of little use if you want advise on rigging a bermuda mast on a boat with a centre mainsheet or a flyaway spinnaker pole system. However, they do still contain some useful advise on basic fittings (either rig), setting up a gunter rigged boat & racing basics.
In order of age, they are:
This is a very interesting 1976 book edited and compiled by Sally Karslake, Mirror Class Assocation Secretary, and publiched by the Mirror Class Association. Sally lived near Hailsham in Sussex. The ISBN of the book is 0903931109. It is a guide to building, crusing and racing the Mirror, with articles and contributions collected from many different authors.
"Sailing The Mirror" by Roy Partridge, published by Fernhurst Books ISBN 0 906754 01 1 published in 1980 and no longer in print. This is a "How to Sail" book specifically for Mirror Sailors. Over 120 black and white photographs and drawings show you in simple logical steps how to rig, sail, tune and race your own boat. No prior knowledge of sailing is required.
"Mirror Racing" by Guy Wilkins, published by Fernhurst Books in 1989, ISBN 0 906754 45 3 and no longer in print. This book is a guide to making the most of this spectacularly popular boat. Using photo-sequences and diagrams, Guy Wilkins describes how to make your Mirror the quickest on the water - if necessary by building a new one - and explains how to fit it out and sail it fast on all legs of the course and in all conditions.