Here are some websites and shops where you can buy film in Hong Kong.
CameraFilmPhoto
Selling lots of different film, like cinestill, Agfa, Rollei everything really and also camera bags, darkroom accessories. Looks like a cool site, but I haven't bought anything from there myself.
http://camerafilmphoto.com/
Meteor
Same here, looks like a good site.
http://www.meteor.com.hk/shop/en/6-films
LOG-ON
Log-On sells Lomo cameras, Polaroid Cameras, Instax products and a bit of 35mm film, but not very consistently. But every time I'm there, I get some Agfa Vista. I think they also will be selling the INSTAFLEX which is available to buy in just 9 days.
City Super Log-On
Yahoo Auctions
is really popular in Hong Kong and it is alright sometimes for buying film or even cameras, especially Holgas, unfortunately it is all in Chinese, but if you already have a Yahoo account you can contact the seller (with some help from google translate) and arrange the trade somewhere. I bought a Minolta HiMatic 7S there once in really good condition and with 3 months guarantee!
Here's a Shop selling Lomo Film
http://hk.user.auctions.yahoo.com/hk/user/lomochanchan
FilMe
http://www.thefilme.com
Stanley Street (or what is left of it)
The shops still left are Miramar next to the Jockey Club in the 1st Floor and the shop at the corner of Pottinger Street
PhotoScientific is now in Sheung Wan
(64 Wing Lok St)
If you know of any other shops where you can buy film in Hong Kong, please let me know.