SubFinder is an application that lets you search for subtitle files right from Finder. It adds an item to the services contextual menu. So, whenever you need to find a subtitle, you can start a search by simply right-clicking on the file and then selecting the "Find subtitles" button. This application only has a few settings that you can change and, since it runs as a service, it doesn't really have a graphical user interface. When you launch its .app file, you will be accessing the Preferences window directly. From here, you can tell the application to automatically rename any subtitles that are downloaded and to close itself when the operation is successful. Also, you can set your desired subtitle language and where the app should search for subtitle files. The two available sites are Addic7ed and Subscene. I hadn't heard about the former, but I use the latter all the time and it has most of the English subtitles that I need.
In my testing, I was unable to get the application to work. At first, the Find subtitle option wasn't available, but there is a fix for that on the developer's website. Even after applying it, though, I got an error every time I attempted to find a subtitle.