Use your imagination and create a Pocahontas costume yourself. Choose from one of the many fantasy versions of Pocahontas. Then look for fabric that resembles the hide of an animal. For an authentic look get actual deer hide as long as there is enough material to make a skirt with fringe and halter top. A full leather dress is another option. The pattern can be crudely cut with rough edges.
The shoes have to be moccasins or nothing at all. This is not always convenient in the colder states. Halloween can have snow on the ground, so actual moccasins are the best way to go. If there is no way to find a pair of moccasins, try making a faux pair. Look for the thickest ankle-length brown socks you can find. Attach strips of fringe around the top, then try weaving leather lacing around the top of the foot to give a handmade look. Slip over little shoes or wear as is. Use long socks for moccasin boots. Attach fringe at the top and running down the sides. Decorate with symbols and beads to give them an authentic feel. Wear a turquoise or stone necklace. Your hair should be long and black; if it isn't naturally, look at costume shops for long black wigs that can transform you.