I hope someone comes up trumps for you, but if you are stuck, shift dresses, the type Twiggy wore in the sixties, are very easy to run up, for anyone with basic sewing skills. It doesn't even need to have sleeves, Just chose a bold fabric.
I'd happily design one for you myself, but these days my seams aren't up to much.
By the way, please post when tickets are going on sale, as I can't wait to see the play.
