As far as I found out, you can only download jhbuild from cvs.
$ cvs -d :pserver:<email address hidden>:/cvs/gnome login
Logging in to :pserver:<email address hidden>:2401/cvs/gnome
CVS password: press enter
$ cvs -d :pserver:<email address hidden>:/cvs/gnome checkout jhbuild
$
As far as I found out, you can only download jhbuild from cvs. :2401/cvs/ gnome
$ cvs -d :pserver:<email address hidden>:/cvs/gnome login
Logging in to :pserver:<email address hidden>
CVS password: press enter
$ cvs -d :pserver:<email address hidden>:/cvs/gnome checkout jhbuild
$