Somewhere in your folder structure there is a folder called notifications. Make sure the file is in that folder. It would probably be in the root of the SDcard partition of your phone.
Also, I'm pretty sure that you can add your own notifications folder on your MicroSD card and that will allow that tone to appear in the notifications list.
Beware, the file name matters so make sure you know the name of the file. It will appear alphabetically in the list of ringtone names.