[CentOS] no kernel-debuginfo or source RPM for kernel 3.18.21-17

I'm trying to debug what I believe to be a kernel bug
(https://lists.centos.org/pipermail/centos-devel/2016-March/014463.html)
and I'm trying to set up systemtap for that.

I'm trying to set up systemtap on kernel 3.18.21-17.el6.x86_64 (Xen
4.4.3-10.el6) and it requires the kernel-debuginfo package, however I
cannot find anywhere package
kernel-debuginfo-3.18.21-17.el6.x86_64.rpm. In addition, I cannot find
anywhere the kernel source RPM in order to build the debuginfo RPM.

Should these packages be available in the first place? Am I missing something?

-- 
Thanos Makatos