Ringtones not in iMac Contacts list.

The Contacts list on my iMac doesn't show my custom ringtones. The Contacts list on my iPhone does? So, I'm constantly losing my custom ringtones off my iPhone. It doesn't matter which model iPhone I'm using, it's been happening for years. The ringtones were created using Garageband and are listed in iTunes. What do I need to do to get them into my Contacts list on my main computer? Getting tired of putting my custom ringtones back in my Contacts list on my iPhone!