If Flyfishers Paradise doesn't have them, try Slate Run Tackle and Otto Bookstore in Williamsport. But it may be out of print.
If you are just looking to read the book, rather than buy it, just go to the nearest public library, and get it through inter-library loan. Don't hestitate to do this. It's a normal function of the public libraries; they do this all the time.
It's an excellent book. I think you'll really enjoy reading it.