Its Sonarr, not Solar (NzbDrone has been renamed to Sonarr). There is no package because they haven’t added it yet and the existing NzbDrone package is very out of date (6+ months old and doesn’t have updating capabilities).
Did you look at the link I posted above? I added a section specific to Synology (and a note specific to those running 2.0.0.1397):
Install those two packages I linked and everything should be updated first, you will want to backup your database and configuration file first to be safe, you can get the path to it in System → Info (within the Sonarr UI), they’re in the App Data folder.