Hit up a program called Soulseek. It's like Kazza sorta, and they have their own GBA room where lots of people have all of the games. You can also hit up <a href="
http://www.pocketheaven.com" target="_blank">www.pocketheaven.com</a> for a release list of all games available.
Also if you didnt know, you can run an 8-bit Nintendo emulator on the gba, and can store loads of games on a flashcart. All info can be found on the previously mentioned site.