gmsh-1.63.0-source.tgz does not exist at the master site.
Update to the latest version 1.63.2.
=> gmsh-1.63.0-source.tgz doesn't seem to exist in /usr/ports/distfiles/.
=> Attempting to fetch from http://www.geuz.org/gmsh/src/.
fetch: http://www.geuz.org/gmsh/src/gmsh-1.63.0-source.tgz: Not Found
=> Attempting to fetch from ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/distfiles/.
fetch: ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/distfiles/gmsh-1.63.0-source.tgz: File unavailable (e.g., file not found, no access)
=> Couldn't fetch it - please try to retrieve this
=> port manually into /usr/ports/distfiles/ and try again.
*** Error code 1
Stop in /usr/ports/cad/gmsh.