I received the fan duct file from Cetus because my fan duct was broken. The STL file I received had errors somehow and wasn't printable. So I used that as a base to repair it/design my own with thicker areas to make the duct stronger.
Edit: this is apparently for the pre production Cetus 3d printer. Cetus has just released the new spare parts: https://www.cetus3d.com/ueditor/php/upload/file/20170204/1486180208895795.zip (thread: https://www.cetus3d.com/community/forum.php?mod=viewthread&tid=119&extra=page%3D1)