Try Horticultural sources...
The Grafters Handbook, R.J. Garner. Published in Association with The Royal Horticultural Society.
This book goes into many facets of prunning not covered by any Arborist publication that I know of, remember horticultural practices have been around for alot longer than Arboricultural teachings...
There are many, many other authors outside the realm of Arboriculture whom have been writing about prunning techniques for longer and more vigorously than all or any of the supposed heroes of Arboriculture, dont be blinded by the hype...
Practice your own techniques and journal them, every perspective enlightens us all...