All the images I have seen of fringed Irish scabbards date to the 1500s, or Early Modern Period. There are no surviving examples. The core would be speculative. I had one reproduced this summer and had the maker use thick leather for the core and a softer thinner outer covering that was fringed all around. I think others have used wooden cores.
"...The O'Brennans, a sept of thieves without any right or title, ... were a perpetual disturbance to the peace of the county,"