There is also a keyboard seller just a few units away from the Black Cat Courier.
It is located along Bade Road, and you can see Ducky's Office not far from there.
I've found FILCO, Ducky and Realforce in there.
Or you can try to visit ArmyGroup. They have FILCOs and Realforces for sale.
The entrance is pretty hard to get into, but if you ask the guard at the ground floor, he should be able to guide you right in.
It is right across the street from Guanghua digital plaza, on a corner lot just above a courier service office.
Right across the street is pretty subjective though. I recalled having to walk across 2 or 3 streets to reach there.
ArmyGroup Address
台北市松江路二號二樓之五
Second Floor, unit 5, SongJiang Rd, Taipei City
By the way, Ducky's office is located along Bade Road. The Songjiang road address seems to be the older one.
You can try to get a Google streetview of the location anyway if you want to learn your way around before going there.