To get Maria theme you don't need a GBA for maria's theme in this version. you can buy it from the black market after getting 180 emblems for 30000

Amy's theme is sold at the black market for about 20000 rings after win at least two emblems that have to do with the Chao races get everyone's mission emblems They do not have to be "A" ranks.

Omochao's theme is at the black market for around 10000 after You need to have at least 100 emblems

You can get the secretary menu screen to get it go to the place where you choose a menu screen and rotate the control stick in any anticlockwise for one minute

In the end the chao black market is very random so if it they do not seem to wark go to the chao black market again and again and again