I won this hat in Week 95 of the It’s A Wrap! Star Trek auctions on eBay.
Two of these White Priestesses can be seen in Spock’s fal-tor-pan procession in Star Trek III: The Search for Spock.
Update: As of July 10, 2010 this item is no longer in my collection. I sold it to Star Trek Prop and Costume forum member, David.