Hi, I live in HK.
AFAIK there is only one shop in HK which officially carries any Inon stock, they are at www.chinesediver.com. I have only been in there once, and they are not always enthusiastic about answering my telephone enquiries.
Occasionally Diving Adventure in Causeway Bay has something which has been purchased in Japan and brought to HK unofficially.
I order my Inon stuff directly from Japan.
I would think you have some chance of getting the Olympus/UN WAL at ProDive in WanChai (www.prodive.com.hk or +852 28082819), or at Wing Shing Photo Supplies in MongKok (+852 23966886 / +852 23966961). Actually ProDive is the only big dive shop in HK which is really serious about uw photography support. Second best is Diving Adventure.
If you want to call Wing Shing you should try to call weekdays between 11:00am and 5:00pm HK time. They are all open 11:00am-9:00pm 7 days but outside the times I mentioned they will probably be too busy to pay attention and will be very unhelpful. (That's my experience, anyway.)
Of course, not speaking Cantonese, I may have missed something useful.
HTH
-David