An archive of old packages (3.3.2 and later) for Debian/Ubuntu-based systems is available here: https://apt-archive.postgresql.org/

Old versions can be located with e.g.:

          yum --showduplicates list repmgr96

(substitute the appropriate package name; see CentOS packages) and installed with:

          yum install {package_name}-{version}

where {package_name} is the base package name (e.g. repmgr96) and {version} is the version listed by the yum --showduplicates list ... command, e.g. 4.0.6-1.rhel6.

For example:

          yum install repmgr96-4.0.6-1.rhel6