Neat to hear this might be a rare one. Some of the more typical Mandara region pieces have a similar "celtic" look Gav.
I find it quite attractive.
The closest thing to this dagger I can recall is a piece of Wolf's, which I'm sure he won't mind if I link to his site.
http://www.africanarms.com/all-album...4101-93246784/
http://www.africanarms.com/all-album...38/mode/matrix