There are a few wood shops in Wellington Street. I use a guy called Sam, 3 doors down from the 7-11 at the corner of Wellington and Aberdeen.
Most wood shops in HK sell notched 2" x 1" for partitioning, might be ok if you varnish it.
Otherwise ask for San Jungh hardwood. What with HK's weather, wouldn't you be better off using the re-constituted plastic wood ?
There is a chain store called Mings (?) who have shops everywhere. Wanchai's Thomson Road or Mongkok's Reclamation Street.
Or we can build it for you. Renovations Hong Kong Limited.
Good luck,
Phil