zisofs-tools is now at version 1.0.4; the latest on Portage is 1.0.3 . The source files for v1.0.3 are no longer present at SRC_URI. A simple copy of the ebuild should suffice.
done http://cvs.gentoo.org/cgi-bin/viewcvs.cgi/gentoo-x86/app-misc/zisofs-tools/zisofs-tools-1.0.4.ebuild?rev=1.1&content-type=text/vnd.viewcvs-markup