Numerous books have been published about real tennis. Ronaldson Publications dedicates its output to real tennis and an excellent resource for other tennis books is The Tennis Bookshop.

The most authoritative and recent book on tennis around the world is from 2015: The Neptune Book of Tennis & Racketsby James Bruce. Most clubs will have a copy of this tome lying around. 

Many clubs will also have copies of other, seemingly random tennis books lying around. If you are trying to create your own tennis library and neither Ronaldson Publications nor The Tennis Bookshop can help you, second hand book websites, eBay or Amazon are probably your best bet.

Finally, newsletters and annual reports are widely produced by clubs and national associations for their members. Examples include Chase the First and an annual report from America and frequent T&RA newsletters. The T&RA also produces a print report once a year which is sent to all members, but can also almost certainly be found in every UK club.