If you do a search at www.rinkya.com you can 
look up GameBoy Advance games.  There is also 
www.lik-sang.com which sells quite a bit of 
import games.  eBay also carries them (do a 
search under 'import games'.

Just for future reference:  this is a cels forum 
and some people get kinda annoyed when topics 
other than anime cels are talked about.  This is 
just fair  warning as there may be flames to 
follow.  ^_^;

Good luck!

jINx