Corn husks may be a viable option for a potting material, if you don't have anything else available. I am afraid that the husk would break down so quickly that it may not be a good idea...just my two cents. Also, the texture of the corn husks you would use (how finely it is chopped) depends on the orchids you are growing...for catts, you would use a more coarse (larger pieces) because they like to dry out. For terrestrials/phals/other similar types, you could use a more finely chopped media because it should hold more water.
Coir (coconut) has been used successfully for many types of orchids, but one must be careful because it holds a LOT of water and does not dry out as quickly. Watering should be reduced when using this medium, and one should always insert a finger (or use a skewer) to check if the inner pot is stilll damp before watering.
I am unsure as to where to purchased either of these things, but Im sure others will pipe in if they haven't already!