Many of you know I am good friends with Dana Hammontree, who just recently started a prop business with Wes Cannon, another well known prop collector. Their company is Hollywood History and you should check it out regularly if you are a Star Trek fan. I recently bought a set of Tellarite pistols from them and I give Dana high marks for his service.
Dana is as connected as any dealer in the Star Trek prop and costume market (I met Dana waiting in line to get into the Christie's Star Trek auction in 2006) and so he tends to have good Star Trek items for sale. One such item is a Klingon Mask from Star Trek VI he just listed.
If you don't have one of these, I highly suggest getting this. It is listed at only $ 899. I think that is a great price for a real mask used on Star Trek and it comes with an IAW COA, so you know it is the real thing.