CentOS install proftpd with yum
You have to install it via EPEL
http://dl.fedoraproject.org/pub/epel/6/x86_64/repoview/proftpd.html
You can grab the single RPM or install the EPEL repo as follows
rpm -ivh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-5.noarch.rpm
yum update
yum install proftpd
yum list available proftpd
if you cannot find it, then your repo does not have it.