I couldn't find the d-apt-keyring package anywhere

root@d9:~# cat /etc/apt/sources.list.d/d-apt.list
deb http://master.dl.sourceforge.net/project/d-apt/ d-apt main #APT repository for D
root@d9:~# LANG=C apt-get -y --allow-unauthenticated install --reinstall d-apt-keyring
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package d-apt-keyring

Cf.
http://d-apt.sourceforge.net/
https://sourceforge.net/projects/d-apt/files/dists/d-apt/

Meanwhile I just use http://downloads.dlang.org/releases/2.x/2.077.0/dmd_2.077.0-0_amd64.deb ...