I just solved the same problem
In software manager, click Edit/Source (I'm using the Chinese UI so I am not sure what it is in English)
Choose "Other software" and then click Add
Select one Debian reop from
http://www.debian.org/mirror/listI entered "deb
http://ftp.tw.debian.org/debian/ testing main contrib non-free"
Then you will see 0AD in the software manager
Have fun
