Hi - what a glorious dress!!! I think I might have to try something similar.
Going back to the original pics, I think it's actually not very complicated. It looks to me a half handkerchief dress with an extra layer just tacked on underneath the hem of the main dress. I think you could adapt it quite simply from any sheath dress pattern or even just a sleeveless bodice pattern as has been suggested before. I tried to draw it (attached - sorry it's a rubbish drawing).
Basically I think they put massive godets at the sides of a normal sheath dress without reshaping the hem to compensate, like a half handkerchief shape. That makes the sides longer than the front. The back is the same, so you get just two points, not the four of a handkerchief. There's no front seam and no shaping of the hem line, it just makes that shape itself. Then you add another layer underneath cut as a straight piece from the same border fabric. This is longer than the upper layer and attached loosely like an informal curtain and ruched up at the side seams a bit more to give extra fullness. In her dress, you can see how it's attached quite clearly as there are little gaps (the peachy bit in the front view is thigh, and the gaps are obvious in the side view).
Railroad the fabric and cut the front on a crossways fold (or flip the pattern) and put a seam at the back. You need the selvage to be the hem on both parts.
For length, I think I'd start with the upper part ending about crotch level at centre front and just above the knee at the side, then an under layer of maybe 40cm. It really needs a border fabric to make it work and the depth of the border will be important in the final lengths. How much difference you give between front and sides will also make it wider or narrower. More difference will give more width as the sides drop more.
Looking at the pics, for the pinky/white version she wears, the scallops are part for the fabric, for the gold version I think they created that scalloped shape on the selvage edge, then proceeded as above.
No idea about a similar commercial pattern, but it would be very easy to make your own pattern.
Can't wait to see the results!