Looking at the material of the tunic its either soft leather or swade.
It doesn't look too dificult to reproduce, a little stichwork and some gluing.
I'd start by searching ebay for those , even look at womens bags or jackets (they're often a soft leather, bags are often quite thin too).
Try going to your local material stockist, they might be able to point you in the direction of a supplier/company that will have the materials that your looking for.
Unfortunately this is the hardest part of the process, and believe me its worth the legwork to the finnished item if you put the time in first.
It does get easier too, as you go along, you find sites, directions you didn't think of going down, you kind of develope a sixth sense as to where stuff might be, and finally always ,always keep you eyes open, you never know when you might spot something that you can use.