Upstream has a passion for removing old tarballs from their server and gentoo doesn't mirror their files. sip needs to be updated regularly to workaround this.
*sip-4.5.2-r1 (23 Dec 2006) 23 Dec 2006; Tiziano M
*sip-4.5.2-r1 (23 Dec 2006) 23 Dec 2006; Tiziano Müller <dev-zero@gentoo.org> -sip-4.5.2.ebuild, +sip-4.5.2-r1.ebuild: Fixed bug #155754. Corrected dependencies. *sip-4.5.2 (20 Dec 2006) 20 Dec 2006; Markus Ullmann <jokey@gentoo.org> -sip-4.5.ebuild, +sip-4.5.2.ebuild: Version bump
Ouch, my bad for not checking online. My portage wasn't in sync due to eix-sync changing location from /usr/sbin to /usr/bin. Sorry for the noise.