I resently purchased some metal ones w/coating on them for my natural girls from Icings aka After Thoughts. My girls have broken some of the plastic ones so it just a waste of money. They also have a few leather type ones as well. The plastics can be found just about store that has a hair care section. The leather ones I purchased from Walmart.
Though I'm not natural, I also have an assortment of stretchy band types. The ones by "[R] Accessory Co." resemble a popcorn and a snood type pattern, possibly made of satin ribbons, purchased from Value City. The other ones by Conair, Vidal Sassoon, and etc. purchased from Walmart, Kmart, etc. Materials unknown only the very narrow ones might possibly be made of a polyester or a satin like material.