If you still have a DS: http://filetrip.net/f3228-GBA-Backup-Tool-0-21.html

 

The only ones that plugged into a gba were those like:

F2A usb cable/P25 cable: only available from another user in the trade section
EZFA usb cable: no longer available, http://shop01media.com/info.asp?ProductID=13661

The game bank device isn't available either.

You can use sites like tototek to see if they ever stock any retro stuff. You might be waiting A LONG TIME.
http://www.tototek.com/store/


You can make your own cable if you take the time to make one. The xboo cable doesn't dump games. If you want to make one anyways:
http://chishm.drunkencoders.com/SendSave/index.html