Previously created iOS ringtones, 2017 and older have been posted as .mr4 on this site. They are listed as Tables 1 and 2 accessable from the drop down menu "iOS Ringtones" on top of the linked page at the end of this post . These <=2017 ringtones require older versions of computer-based iTunes which allow installation of custom ringtones onto the Apple mobile phones. Apple, however, no longer provides the option in the new and latest iTunes.
A viable option and perhaps a more efficient way to create and install "roll-your-own" ringtones require two things. One, the iPhone must run on the iOS 11 platform; it which includes Files App with the iTune Drive. Two, the Apple GarageBand app (free download from the App Store) must be installed on the iOS 11 capable iPhone.
Table 3 of 3 listed the 2018 Ringtone-ready MP3 for your iPhone ringtone creation. On the page's menu bar, access this table from the drop down menu labeled "iOS Ringtones."
Today, 25 March 2018, two ringtone-ready MP3 files posted are:
Frankie, Carle - #01 "Andalucia" (256 kbps)
Frankie, Carle - #02 "Green Eyes" (256 kbps)
An image of the table where the MP3s are posted:
If you like a posted tune, download its MP3 from the link below by using your Mac or PC. Upload or export the MP3 to iCloud Drive at
icloud.com. Then use the GarageBand app app 2.3.x on the iPhone directly convert the MP3 at the iCloud Drive to a ringtone onto your device.
The GarageBand app can also remove any ringtone it created on the iPhone.
Click on this link to the iOS iPhone Ringtone Page