Currently there is no ebuild for the ices0 stream source from www.icecast.org There is an ebuild for ices version 2, (media-sound/ices) but ices2 does not support mp3 streams, only ogg.
You can grab it here; we are not adding obsolete version into the tree. http://sources.gentoo.org/viewcvs.py/gentoo-x86/net-misc/ices/?hideattic=0