In a few days I will release the latest version of PluginManager. It will have a new feature called Manual Plugins, where dead/old plugins will show up that are already listed in the directory that may not be compatible with your Kanboard. However, instead of installing, it only allows you to download the plugin so you can go through it and see if it is worth manually installing. You might find something useful there too.
https://kanboard.discourse.group/t/new-plugin-pluginmanager/