Check the official websites.
For example, directly from nintendo.com you can get new game cases for Wii, Gamecube, DS for 1 dlls each. You can also buy original instruction booklets (even from N64 games), or parts for your systems.
I have bought a lot of used with boxes in bad conditions, and from Nintendo.com you can make a used game look like new ordering a new box, cover and booklet.








