The word is generally written in hirigana as . They're sometimes called Pokkuri or Koppori. Both words are onomatopoeia, that is they represent the sound of walking in them.
Pokkuri and Koppori are usually very ornate and worn by young girls on shichi-go-san (7-5-3) which is a celebration at ages 7, 5, and 3. Okobo are generally quite plain, made of unfinished wood. The color of the straps indicates the rank or experience of the woman. Starting off with red and ending their days as Maiko with yellow before becoming full Geisha. Geisha don't wear Okobo, they wear either geta or zori.
Real Okobo seem to be only available in Kyoto and are very expensive, starting at about 50,000 yen or $450. Coupled with language, money, and distance problems, even if I could afford the price, they'd still be hard to get. Another problem is they just aren't made to fit big American feet.