Comment 2 for bug 102018

It is available here: http://xorg.freedesktop.org/releases/X11R7.2/src/app/lbxproxy-X11R7.0-1.0.1.tar.bz2

That is the proxy program itself. The extension to enable it server-side still resides in the server code, and according to http://packages.ubuntu.com/feisty/libs/libxext6, it is still enabled (that is, libxext6 includes the lbx extension).