I broke down and bought fabric.
It's a silk and rayon blend brocade. I love the chocolate and black colors, and the pheasant motif is most pleasing. The smooth brocade feels right for the corselet, since I want a slick fabric so a light, 20's flapper's dress will glide over it. I could probably use this fabric on it's own, it's feels heavy enough to do the job of a thin cotton broché, but I think I should back it with a lightweight batiste. Not for strength so much as for cleanliness. It seems wise to have a layer of cotton against the skin instead of the brocade. I don't think I'll fuse them together, just flatline.
I also have the garter clips and grips.
I still have to do one more fitting with the mock-up to fit the gores, but then I can cut into my pretty new fabric!