I have created a new port for net/samba412, based on samba411.
The port has only been tested with a few combinations of options, but since the changes relative to the previous version are not that big, I assume that it will work for most settings.
It contains empty patch files as markers for patches that are in net/samba411 but are no longer required in net/samba412.
I have not checked whether the man-pages in files/man are still fully applicable to this version.