In my opinion this is a Sewar, not a Tumbuk-lada. Tumbuk-lada have a significantly thicker hilt with a flater pommel.
I think it might be rhino. Rhino horn was fairly frequently used for sewars. I have at least one if not two rather muddane sewars with rhino horn hilt and top part of the scabbard.
Rhino horn under magnification has a fibrous structure as it is practically compacted hair.