On the Windows installation CD that came with your computer. If you don't have that, you could have those files already if you computer has the i386 folder under your C: Drive. That folder contains all the files found on the Windows CD.
The East Asian Language support files are locate under the D:\Windows\i386\lang directory. When the wizard asks you for the CD, just browse to the folder and select it.
If you don't have the folder, you can download it from the internet. Here's a torrent for the files:
East Asian Language files