That is the Buck sheath. I had kydex made for my Buck. I had to heat and expand the liner to hold the Mutt. I don't know if Buck has the sheaths available or not. But my Dumpster Mutt CG would fit it, too. I sold my CG, preferring the UM.
I have a few Rainwalker kydex sheaths for my DMDC and DMLE. They are excellent.
I might just get Jeff to make me one for the DMCG then... kydex or leather???? ahhh the choices.