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.