It seems that the mirrors are now all sync'd with the binary RPMs, but where are the source packages? The source RPMs are available for the few packages updated since the upstream 5.3 release, but the SRPMS for the release itself are missing. Example: http://mirror.centos.org/centos-5/5.3/os/ has directories containing the x86 and x86_64 binaries, but should also have a SRPMS directory.