My favorite site for free downloads of books in pdf format that I read on my Nook is archive.org. They have over 300 titles on fly fishing and some on fly tying, fly dressing, salmon fly as well.
" Fishermen, hunters, wood choppers, and others,
spending their lives in the fields and woods,
in a peculiar sense a part of Nature themselves,
are often in a more favorable mood for observing her,
in the intervals of their pursuits,
than philosophers or poets even,
who approach her with expectation."
Henry David Thoreau