Flook's book is absolutely essential but is out of print and can be hard to find. This website has excellent information:

Fairbairn Sykes Fighting Knife First Pattern

This takes you to the 1st Pattern information, links to information on the 2nd and 3rd Patterns and various scabbards, markings and post-War production knives (not all are "fakes") are at the bottom of each page.

The Faibairn-Sykes fighting knives can be considered costly but are surprisingly common.