Sim City, 47-51 Shantung Street.
http://www.tincheungcamera.com.hk/contact-us.php
This place has quite a few retailers of 2nd hand and new cameras. And given your history with cameras, you shouldn't have too much problems testing the 2nd hand lens. I'd definitely have a look atSim City prior to purchasing.
Having said that, I just purchased a Nikon 35mm f1.8 at Man Shing. If you're looking for any official imports in Hong Kong, they're likely to have it. Man Shing is at: 104-106 Tung Choi Street, Mongkok.