The easiest way to find modern ballroom music is to search for something like "dancesport waltz" (or whichever specific dance you are looking for) on Spotify. They have plenty of playlists which are used in studios all around the world. Not all the tunes are modern, but there'd be enough of them to not to have to search for too long. You can also check out vendors such as Casa Musica and DSI London: they sell CDs and MP3s; look for the latest releases though, lots of their stuff is straight back from the 70s...