From Mahara Wiki
Where to download things
|Extra Themes||https://mahara.org/group/mahara-themes and https://wiki.mahara.org/index.php/Themes/Contributed_themes|
|Source code||See https://wiki.mahara.org/index.php/Developer_Area/Source_code|
|Latest dev build||https://github.com/MaharaProject/mahara/archive/master.zip (expect it to be unstable)|
Older versions of Mahara may be available to install as packages in Debian (and its derivatives such as Ubuntu). However, these are very old and are no longer updated or supported by the Mahara Project.