I think this could be quite interesting for the history of the sling:
Last year I participated at a ball in Zürich. There was also a show group which performed a peruvian folk dance (called Valicha) and I was quite astonished as I saw that they used slings to dance. As a friend of mine is a member of this group I was able to have a look at the slings: They were using woven wool slings similar to
http://www.seekyee.com/Slings/gallery/peruvian1.htm (Thimoty Potter)
Although the finger loop was to small to get one of my fingers through (and I have quite slim ones). I was also told, that they all don't know how to sling. Further it didn't seem that the slings were ever used to actually sling a stone.
Some resources:
Dance I saw:
http://www.americabaila.ch/html/de/repertoire/Peru.html (look for Valicha (Huayno), there is a picture)
Unfortunately their youtube video isn't available anymore.
Videos from other groups with the same song and also slings:
http://www.youtube.com/watch?v=Eez6T49YE0khttp://www.youtube.com/watch?v=YZyctNW9RtAhttp://www.youtube.com/watch?v=_N5MvcA9g-IIt seems that Valicha is quite a common and widespread dance as many videos from different groups can be found, and in every one slings are used.