The snapshots repo URL on the SeamFaces module page (http://seamframework.org/Seam3/FacesModule) seems to be out of date and only seems to contain builds up to seam-faces-3.0.0-20100618.
It points to:http://oss.sonatype.org/content/repositories/jboss-snapshots/
but as far as I can tell it should be:https://repository.jboss.org/nexus/content/repositories/snapshots/
... as that has recent builds.