there seems to be endless 'authentic' ones, everyone I know seems to own one that is 'authentic', as well as the drapery dress from GWTW, the maltese falcon and there seems to be about 10 authentic ten commandment tablets around...actually I just think everyone keeps lying to me :P
Some of the Wizard of oz costumes and props were destroyed in a fire (including 1 of Dorothy's gingham dresses ) at the land of oz theme park.
http://en.wikipedia.org/wiki/Land_of_Oz_(theme_park)