Download Free online or purchase a printed copy!
The Parachute Recovery Systems Design Manual by Theo W. Knacke is the design standard for parachutes. More than you need for rocketry but a great resource.
Originally printed in 1991 on contract to the US Naval Weapons Center at China Lake, CA, this book now approved for public release from the US Navy and is available free for download direct from their site.
If you prefer a printed version, spiral bound, it is available here for purchase. This is a printed copy of the file and contains all marking, black spots, and black areas.