This map was found in an online article of MilkX Monthly Magazine whose first issue was published in September 2006. I added several street names and district names to the map and hopefully readers will have a better idea of where the department stores were located. While the map is not to the scale and the locations of the department stores might not be correctly positioned, it nevertheless covers all the Japanese stores that existed in Hong Kong in the 2nd half of the 20th Century.
The URL is http://www.milkx.com/zh/living-culture/THE+GOLDEN+AGE+OF+JAPANESE+DEPARTMENT+STORES+IN+HONG+KONG+
ERRATA
In the above article (in Chinese), the official English name of 東急 should be Tokyu and not Hankyu (阪急), although they may be somehow related as a conglomerate.