I just finished upgrading my third mountain bike from 7 to 9 gears, with the usual stuff replaced and renewed at the same time (shifters, crank, BB, cassette, etc).
I bought all stuff in a bike shop called Velo House in Sanchong.
A bit further away, but perfect to pass on a workday ride up the riverside.
They have a LOT, although little top-end, are most of the time rather cheap, and are easy on replacing.
Their English is limited to non existing though.
It is only the typical cramped shop where you don't want stay too long, so I check online first, have my wife calling if they have it (so far they never disappointed), then I pick it up on a ride.