If you manage to pick up a copy of The List (the magazine that knows) there is a whole section on How to enjoy Hong Kong’s great outdoors.
Also a list (unsurprisingly) of many camping shops.
Issue 10 November 15-30 2005, and can be found at many outlets along with HK magazine. Yes its free.
Don’t forget to read the info provided by Martin William and Charles Frew….again! (pages 20-21).