Firstly, I adore bookstores! I can spend hours and hours in Barnes and Noble's or Border's, both rather closeby.
When I go to the bookstore and want a book on autism, I check out the Psychology aisle, the Self Help section, places where books on medical conditions are kept. Psychological conditions might be a good place to look. Even though ASDs are not really psychological, they lump everything together for lack of better catagorizing.
I spend hours reading books in bookstores. The ones here are more like libraries with lots of eccentric types everywhere studying and reading.
Good place to find eccentric types!
I usually find where books on the subjects I am interested in are, on my own.
You can try the help desk, ask the employee if they have any books on Asperger's Syndrome and where would they be kept? This works for me! They take me right to them. Book store employees around here tend to be really polite and helpful.
My opinion on book stores is that they are a great place to spend half a day in, reading books, thinking, studying if you have something to study, bringing a laptop, writing, researching, term papers, homework, strange people, whatever...they, in general, are very Aspie.
My favorite section of all: art books (including how to draw books/how to paint books all kinds of how-to books)
Anyway, have a pleasant time at yours!