Either locally (Currently in Taoyuan - easy access to Taipei too) or online?
Below is a very good place to find good priced PCs and parts.
Guang Hua Digital Plaza
100 Taiwan Taipei City Jhongjheng District Section 3, ShìMín Boulevard 8號 +886 2 2341 2202
maps.google.com/?ie=UTF8&ll=25.0 … mQWsstCgDQ