That´s an interesting topic. I´ve been searching for alternatives and while I put my mind on kangaroo rawhide for the tsugaru (which, unfortunately won´t happen now), I also bought a parchment (vellum,pergamen) to try it out on an old nagauta. I am far from reskinning the shamisen but thought that I could post pictures of the parchment, if anyone was interested to see how the skin looks like.
Old kawa against parchment
Texture of parchment (back and front)
Thickness of kawa (top) vs parchment 0.6mm (bottom)
p.s. Sorry, I feel like I am all over the forum these past days but I cannot not share if it can help others