Today, we finally got the last-hope overlay into layman's global repositories.xml: https://bugs.gentoo.org/show_bug.cgi?id=408739. You can now add the overlay directly via layman -a last-hope.
For the uclibc-compat overlay, you have to manually add http://gentoo.j-schmitz.net/portage-overlay.xml to the overlay property in your /etc/layman/layman.cfg. After layman -S, you can add the overlay with layman -a uclibc-compat.
