I just found some "sprang" instructions on the 'net, I was thinking of making a pouch from a piece of home made sprang cloth.  It might be a bit stretchy, though.  I'll give it a go, and let you all know how it turns out.

Sounds cool English!

Sprang is a "primitive" fabric construction that looks a bit like a cross between knitting and weaving. The work is actually "braided" but on a frame while the warp is under tension. You know when you are braiding and the free ends want to braid themselves if you don't keep untangling them? That is Sprang. True sprang is always symmetric, and has a "finishing ridge" where the two sides meet when you run out of string.

It was used mostly by the Vikings in uses that we would now use a knit (see my post about knit slings - knitting is a modern invention) You can do some nice openwork patterns, so making a sling pocket from only the body cords should be possible if desired. I wouldn't worry about the stretch - it wil mostly be across the pocket, and since you'll probably need some kind of "frame" or edge anyway, it will only help make the shape a little nicer.

Maybe try Naalbinding as well? I look forward to your report(s)! (and pictures)

Matthias