If you're thinking purely CBD. Then try MYERS, DJ's, Hobbyco (in QVB), Dymocks, Konikuya (forgot spelling, its near Citibank). You might be able to find stuff in Chinatown as well. Try Market city and there's another store called Silly Dreams I think which is located on the ground floor of Harbour Gardens apartments, though I havn't been there for a few months now.

Edit: Myers and DJs are in Pitt St mall area. Dymocks (the big one) is on George Street along with Konikuya. Forgot the street names of the ones in Chinatown.