[CentOS-devel] where did you get the optional packages?

hi, as rhel-6 release my old question arise again. from where did you get the optional packages' src.rpms? eg: a2ps-4.14-10.1.el6 is included in all of this channel: RHEL Client Optional (v. 6 for 32-bit x86) RHEL Client Optional (v. 6 for 64-bit x86_64) RHEL Server Optional (v. 6 64-bit x86_64) RHEL Server Optional (v. 6 for 32-bit x86) RHEL Workstation Optional (v. 6 for 32-bit x86) RHEL Workstation Optional (v. 6 for x86_64) but this packages (with many other optional packages) can't be find on redhat's ftp server (or at least i can't find it). can you tell me from where the centos team legally download this packages' src.rpm? thanks in advance. regards.