I have a pair of Sherpas, same vintage, I use for loaners. Needed tail repairs, coudn't find the real stuff, either. Used strips cut from heavy duty inner tube. Also used strips cut from a length of Coverlight Neoprene from Seattle Fabric, similar to the decking-may have some left I can share-will look tomorrow.
http://www.seattlefabrics.com/vinyl.html#Coverlight%20Neoprene