Você não pode espelhar os servidores, você pode clonar os projetos.
Use o comando awk
abaixo para uma execução a seco
find /var/lib/apt/lists/ -type f ! -name "*.gpg" ! -name "lock" -exec awk '/Vcs-Git/ {print "git clone "$2}' {} \; | sort -u
Exemplo de saída
git clone https://gitlab.uncompleted.org/debian/postfwd.git
git clone https://gitlab.uncompleted.org/debian/ps-watcher.git
git clone https://git.torproject.org/debian/tor.git
git clone http://smarden.org/git/bcron.git/
git clone http://smarden.org/git/dash.git/
git clone http://smarden.org/git/ipsvd.git/
git clone http://smarden.org/git/twoftpd.git/
git clone http://smarden.org/git/ucspi-tcp.git/
git clone https://mod.gnutls.org/mod_gnutls
git clone https://repo.or.cz/r/git/debian.git/
git clone https://www.github.com/ioerror/tlsdate/
git clone http://tcosproject.org/git/p910nd.git
git clone http://tcosproject.org/git/tcosconfig.git
git clone http://tcosproject.org/git/tcos-configurator.git
git clone http://tcosproject.org/git/tcosmonitor.git
git clone http://uv-cdat.llnl.gov/git/cmip5-cmor-tables.git
git clone http://www.project-moonshot.org/git/moonshot.git
git clone http://www.project-moonshot.org/git/moonshot-ui.git
e este comando para clonar os repositórios, no meu caso 11,818
mkdir -p ~/src
mkdir -p ~/src/mirror
cd ~/src/mirror
find /var/lib/apt/lists/ -type f ! -name "*.gpg" ! -name "lock" -exec awk '/Vcs-Git/ {system("git clone "$2)}' {} \; | sort -u