Get both Veverka's and Shewey's books on spey (and dee) flies. Together they will provide you with a master's degree (if not a Ph.D.) in the history, materials, and tying of these flies. Shewey's STEELHEAD FLIES is very short of spey and dee technique.
Radencinch has great books, but his minimal info on spey and dee flies, although good, is not the greatest. The reason for this is as he admits in his book 20 SALMON FLIES he rarely ties them because he concentrates on full-dressed and modern free-style salmon flies.
Also, although spey and dee flies (especially spey flies) appear to be simple and easy to tie to the uninitiated, they are really deceptively hard to master due to requiring excellent thread control and tying technique to look good. They really should not be tried by novice or beginning level tyers. Intermediate skill tyers (meaning folks who can tie good trout dry flies, spin deer body hair, #18 and smaller dries and nymphs, bucktail streamers, etc. are who should be attempting to tie spey and dee flies through learning from a book. And yes, I know there are exceptions to this and some beginning and novice tyers have started tying spey and dee flies pretty much right out the box, but it is much easier to learn them if you have Intermediate tying skills.