If you will execute sudo apt-get download openssh-server you will get a .deb file that can be installed offline.

However, as there are several dependencies packages that are required by openssh-server you will probably want to download all of them too.

To do it execute this instead: sudo apt-get build-dep --download-only --reinstall -o dir::cache=<path_to_save> openssh-server. where <path_to_save> is where you want the downloaded dependencies to be saved.