The source code and documentation are available at tromp.io.
The most reliable source for this software is directly from the developer's website. Download MCMtromp txt
If the main site is inaccessible, research software is sometimes archived in: The source code and documentation are available at tromp
Searching for "MCMtromp" or "Modified Cahn-Hilliard" in GitHub might lead to community forks or archived versions. Download MCMtromp txt