Possibilities, but...

...and there is always a 'but'.
The search begins for the perfect silk taffeta that will become the Boucher Pompadour gown.
I have not exhausted all my resources yet, this was merely a preliminary search.
So far, this is what I have come up with at www.puresilks.us :

Green (and I mean; holy-crap-we're-not-in-Kansas-anymore-Toto-green!) silk taffeta. This might be way too vivid for what I want, and while vivid colors did happen in 18th century fashion, this just seems too garish. it's one of those I'd need to see in person, in outdoor light as well as indoor. To me, it also seems to have a somewhat warm yellow base tone, whereas I need to stay on the cool side:

And one somewhat 'meh' option is this green shot with light blue. While much softer than it's above cousin, I'm not so sure I want a shot silk for this. Pompadour's gown in the painting does not seem to have a cross-weave color to the silk. At least to me.
Another mark against this particular silk, is the slub that seems to be showing in the photo. Dupioni is a big deal-breaker. Not only to I not like the look of it, I won't go near it for historical projects earlier than the 1950s...and I tend to stay away from the 1950s anyway: