As you may know, whether in Hong Kong or in Mainland China, you will need
many, many business cards. As everyone here has a business card and give it out, you may quickly get out of stock.
There were traditionally two Hong Kong districts to solve this problem, but
one disappeared.
Lee Tung Street (Wanchai area, near Southorn Playground), that still is
recommended in many publications has been destroyed ( if you know Hong Kong and Mainland you won't be so surprised, as everything is continuously under construction).
The second one, however, survived and is located across from the Wing On
building, Sheung Wan (closed to the Macau Ferry Terminal). The "street" is called Man Wa Lane