Unfortunately since the Disneyland Encyclopedia is unofficial, you aren't going to find it in the parks or at WoD. (I looked and could never find it, sadly). I bought mine at Barnes and Noble at the Grove in Los Angeles...and they only had one copy! Your best bet would be to order it off Amazon or a different vendor. Disney won't sell it because it's "unauthorized".
EDIT: Oh, and I might as well put in that the Disneyland Encyclopedia is great! It really covers EVERYTHING about the park. You won't find anything on DCA though. It's strictly Disneyland.