Where can I find the software installers for Master X3 TDM?
The latest version of Master X3 for TDM is 4.0 and it can be downloaded from this page.
For more information about how to update your Master X3 to the latest version, please refer to this answer.
Older Master X3 TDM versions are available below:
Master X3 TDM 3.9 for Mac OS X (PPC) and Pro Tools 6.x