commercial press and popular are the most convenient ones. they dont have the books you want but they have some different kinds of books from time to time so i have to visit there from time to time.
metro got a good collection. it just happens to be a bit expensive in their pricing.
and also the specialist bookstores for children, they have a very wide collection too. just that it is a bit expensive also.
in the book fair last year, i found this Little Rainbow Educational. i mail ordered some osbourne readers through them once. http://www.facebook.com/littlerainbow.com.hk
also from the bookfair did i spot this store: http://www.funtoread.com.hk/ read from some magazines that they do have their outlet opens from time to time. but i hv only bought from them at the bookfair
i am also looking forward to the book fair in summer. there we can find everything from the same one location. :)