I tried looking for Not Installed plugins but they do not show up on QGIS version 2.18. Under Plugin Settings, QGIS official plugin repository is shown as unavailable. When reloading nothing happens.
(I previously tried using the mmqgis plugin on 3.2 but did not work for most things, I assume that's because the version is not yet stable, so updating versions seems to not be an option in this case)