Default ringtones are usually stored in
/system/media/audio/ringtones. You might be able to access this location using a file manager.
Keep in mind that, residing on
/system, this place is read-only at best without root-access: so while you should be able to copy from here, you cannot place any files into this directory. If you want to manually add ringtones to your device, rather create a similar directory on your SDcard (
/sdcard/media/audio, with sub-directories for
notifications, etc.). This location should be recognized automatically by the Android system.