I am not sure where Verizon purchased ringtones go on the phone... Take a look on your internal and external SD cards for a folder called "Media" inside that folder will be a folder named "audio" inside that folder will be 3 folders "alarms, notifications, ringtones"
Find the ringtones you want to use for notifications and copy>paste into notifications folder.
Download an Mp3 ringtone creator app and you can make ringtones, alarms, and notifications from any song you want...