Alternatively, you can download a free ringtone app for Android and iPhone devices that contain large categories of ringtones to choose from. Some of these apps even walk you through how to create a ringtone from a specific song you already own at https://toqueparacelular.com/
Another option is to simply download a ringtone and then transfer it to your device via iTunes. However, this can be costly if you're trying to transfer lots of songs.
You can also create a ringtone from any music that is stored on your iPhone or iPad by using iMyFone TunesMate, a free application that makes it easy to sync music to your phone. This application can be used to create a custom ringtone from any song in your library.