I just published new 1.812.210.57-1 ISO’s for FreePBX that include the new Asterisk 1.8.12 RPMs.
As always you can download the Distro images from http://www.freepbx.org/freepbx-distro
To upgrade your existing FreePBX Distro please see http://www.freepbx.org/forum/freepbx-distro/distro-discussion-help/stable-release-versions