Hey mate, I went to hong kong this year. Tis a bit tricky getting speciality parts like that. The only place is the northern end of Mong Kok that I could find, i'm sure there's better but that's a good place to start. Also they don't really drive nissan turbos there, lots of toyota and honda so it can be a real challenge getting anything nissan, that said there are some nuts GTRs too.
There is a hong kong skyline forum which you could ask on but I seem to have lost the URL (I left it on a PC in HK actually ).