The branches have been removed by upstream. So I guess ebuilds should be removed as well.
These are possibly insecure as well.
+*zen-sources-3.10.9999 (12 Jul 2013) + + 12 Jul 2013; Markos Chandras <hwoarang@gentoo.org> + +zen-sources-3.10.9999.ebuild, -zen-sources-3.6.9999.ebuild, + -zen-sources-3.7.9999.ebuild: + Version bump. Remove old ebuilds. Bug #475898 +