Slacker's catalog is pretty bad, but they do have "some" Beatles tunes. With the standard Slacker subscription that comes with a Tesla it's very hard to get to hear some artists. I guess their contracts are too expensive for Slacker to play them.
I've between playing The Beatles on Slacker since Christmas Eve. Did a voice command "Play The Beatles," scroll past all the songs to Artists in the pop-up and there you go. Like all the Slacker "stations" you will get a variety of other artists.
We have it. I've been listening to the various Beatle stations. Just log in via the Slacker mobile app or web page with your Tesla credentials and find the Beatle station you want and select "Add to My Music". When you go to your car the station will be in your favorites like below.