How do I transfer purchased iTunes ringtones from my iPhone to my computer?

How do I transfer/sync purchased iTunes ringtones from my iPhone to my computer?

I've found a lot of answers here on how sync from computer to phone--that I know how to do. But doing just the opposite? There does not seem to be an intuitive solution.

If you purchase movies and music on your phone, and iTunes automatically downloads those medias to your computer, then why doesn't it do the same with ringtones purchased on your phone?