You can download Plex.Earth 4 for AutoCAD 2015-2021 from the following link:
This is frequently updated and can always be used to download the latest release of Plex.Earth 4.
If you are using Plex.Earth 3 for AutoCAD 2010-2018, its latest release (version 3.6.5991) can be found here:
Note that due to it being based on an older framework, Plex.Earth 3 will no longer be developed, 3.6 will be its final build and AutoCAD 2018 that last version it supports.
You can contact us at firstname.lastname@example.org for any additional information you might need.