You can get the official versions of these files from several places. You can use whichever is the most convenient for you.
gnulib project on savannah.gnu.org, which you
can access via anonymous Git or CVS. See
https://savannah.gnu.org/projects/gnulib.
The official Texinfo sources for the licenses are also available in those same places, so you can include them in your documentation. A GFDL-covered manual should include the GFDL in this way. See GNU Sample Texts in Texinfo, for a full example in a Texinfo manual.