The STL files for the cartesian robot can be found at:

https://sourceforge.net/project/showfiles.php?group_id=159590

(look for the latest cartesian bot files).

In this directory we are starting to translate these files into 
Art of Illusion so that anyone can easily edit them.

Note that you can import any STL file into Art of Illusion, so you can do
that with the STL files in the Sourceforge repository too.