It appears that most of the sources have appeared. There are however a few sources still missing. These are the ones I've been able to determine so far:
from os:
cmirror-1.1.36-1.el5.src.rpm ofed-docs-1.3.2-0.20080728.0355.1.el5.src.rpm openib-1.3.2-0.20080728.0355.3.el5.src.rpm sgpio-1.2.0_10-2.el5.src.rpm tmpwatch-2.9.7-1.1.el5.2.src.rpm wdaemon-0.14-2.src.rpm
from updates:
avahi-0.6.16-1.el5_2.1.src.rpm firefox-3.0.6-1.el5.centos.src.rpm nss-3.12.2.0-4.el5.centos.src.rpm squirrelmail-1.4.8-5.el5.centos.3.src.rpm xulrunner-1.9.0.6-1.el5.src.rpm
from extras:
perl-5.8.8-18.el5_3.1.src.rpm perl-5.8.8-18.el5.src.rpm yum-cron-0.6-1.el5.centos.src.rpm
from centosplus:
libgdiplus-1.2.5-1.el5.centos.src.rpm
I've looked around and they aren't on any mirror that I can find.
-Shad