Hi Jo,
There are many r/c shops here selling motors, lipo-batteries stuff. Here are two that we go quite often:
Waigo Model
http://www.waigohobby.com/
This shop has more inventories - ask a guy call Ah Kin, he knows everything and is one of our top pilots in electric aircraft racing. But mind you that many items in this shop do not have a list price and the lady sitting in the cashier may charge you astronomically if she wishes!! Generally, their items are more expensive than other shops in HK.
Radar Co. Ltd.
http://www.radarrc.com/
This is a more reliable shop in terms of business practice; they also have good items in electric planes.
Apart from these shops, there are quite a few shops selling brushless motors, some are very cheap, in particular for those Chinese made motors. It may cost only HK$ 60 for just a CD-ROM motor, or HK$150 for a Hacker equivalent Chinese motor.
Enjoy your shopping here!