Install Packages for Old OpenBSD Versions

I found myself running an old version of OpenBSD and wanting to install a binary package when, lo and behold, running pkg_add failed with the message: $ sudo pkg_add rsync Error from http://ftp.openbsd.org/pub/OpenBSD/5.6/packages/amd64/ ftp: Error retrieving file: 404 Not Found http://ftp.openbsd.org/pub/OpenBSD/5.6/packages/amd64/ is empty Can't find rsync Funny, this used to work.