The kernel sources can be found at the official Fedora Core download site under /[FCver]/SRPMs.
Fedora no longer ships with the sources. All the sources can be found on the SRPM .isos, but you can hand pick the ones you want from their download site as well.
You might also look under updates if you have updates your kernel. just look for the SRPM folder under your version number to find the kernel sources.
All kernel sources on this site will be listed as kernel.<ver>_FC<ver>.src.rpm
Hope this helps,