I had the same problem for a formal occasion. I had a good look at the outfits worn by klingon females, including Sirella's outfit and Jadzia's wedding dress and came to the conclusion that they are basically medieval in style.
My own solution was as follows - a medieval dress in dark green suede with Enterprise era sleeves - ie fur and chain mail (I found a gorgeous chenille that looked like fur - it was perfect for the sleeves and I made the gorget out of the same fabric.)
the nice thing is, its not a uniform so does not have to copy anything seen on screen, just be consistent with the styles. and medieval dress patterns are both easy to obtain and incredibly easy to make. you just alte the neckline and the shape of the sleeves a little, use Klingon fabrics, such as leather, suede and fur and you have a stunning Klingon evening dress.
I can't show you the whole dress yet as its not quite finished but heres a close up of the sleeves.
Will post a btter picture ASAP.
