It’s no longer in the default install, but it’s still in the repos. You can list the available Virtualmin modules with:
# yum search wbm-virtualmin
Or:
# apt search webmin-virtualmin
Some are only lightly maintained at this point, though, so keep that in mind if installing something old and weird (like svn…nobody uses Subversion, anymore, so you should at least think twice about using it). Mailman is still pretty active, though, and we still fix bugs in the module because people are still using it…just not enough to make it a default part of the install.