How much are you willing to alter the pattern? I believe there is a modern Vogue sundress pattern that has that sort of midriff shaping, but it has either a wider strap or a halter strap. I think it is 8633, but I will double check!
Also, I hope I am allowed to say this here, Sewing.patternreview.com, has thousands of talented seamstresses who would probably be able to help you find a suitable pattern in a heartbeat. :]