Obsolete packages are removed from the main repository, to keep it clean. Old packages did not follow the same packaging and naming conventions, and will not always interact smoothly with newer versions. However, it is still possible to find them in an archive repository called percona-attic.
To install this repository, follow the directions for the manual Yum installation, but create a file
/etc/yum.repos.d with the following contents:
[percona-attic] name=CentOS-$releasever - Percona baseurl=http://repo.percona.com/centos-attic/$releasever/os/$basearch/ gpgcheck=1