It is hard to find Scifi books in mainstream bookstores, I agree. The sections and selections are small and limited to the authors who are mainstream enough to be recognized.
I'm a fan of the genre, although I don't read as much of it as I used to. I am lucky: my friends own a wonderful SciFi/Fantasy bookstore here called WhiteDwarf Books which has a huge selection. Jill and Walter have an encyclopedic knowledge of the genre, and are really good at helping their customers find writers they like.
BTW, they will mail order books to the US, and elsewhere.
http://www.deadwrite.com/wd.html