This archive hosts historical Debian and Ubuntu packages from apt.postgresql.org since April 2013. The oldest PostgreSQL server versions covered are 8.2.23, 8.3.23, 8.4.17, 9.0.13, 9.1.9, 9.2.4, 9.3beta1, and everything newer.
/etc/apt/sources.list entry for the archive repository:
deb https://apt-archive.postgresql.org/pub/repos/apt DIST-pgdg-archive main
deb-src https://apt-archive.postgresql.org/pub/repos/apt DIST-pgdg-archive main
Replace DIST by the Debian/Ubuntu distribution in question, e.g.
buster, stretch, focal, bionic, ... Available distributions are listed in
/pub/repos/apt/dists/.
To browse directories, be sure to append "/index.html" to the URL.