You can use cornstarch to thicken certain items....but with cornstarch you must first make a slurry using a cold liquid and mix that into your hot liquid. It should come back to a boil for the starch to reach it's full potential. Therefore, with cornstarch we're dealing with something that has to be heated first. (Pastry cream, sauces, stews,etc..).
Xanthan can be used in very small amounts directly into cool liquids and mixed thoroughly until desired thickness.
Have you considered gelatin? I'm sure that is easily accesible. Or when all else fails, order from off the web?
Hope this helped a little!
