At this point, none of the GBA Ambassador games are released. There are a few of the NES releases that have hit the eshop for general purchase - Super Mario Bros, Donkey Kong Jr., The Legend of Zelda, Metroid, NES Open Tournament Golf, and Legend of Zelda II (to be released in November).
As of yet, the GBA games have not been released, and it doesn't appear that they will be any time soon - according to this press release, they are concentrating on Game Boy, Game Boy Color, and NES titles for now.
Nintendo may decide at a later date to add GBA titles for download (as they did with a few Game Gear titles), but as of this time, it doesn't appear that they have any plans to do so any time in the near future, choosing instead to focus on first party titles for the 3DS such as Paper Mario, Luigi's Mansion, etc, and VC titles from older systems that predate the GBA.