here's one from Boden...i swear they had a brown polka dot one too, but i don't see it on their site anymore. it definitely seems like the kind of thing they would have though...so if you're willing to wait, i'd check back.
I saw one at H&M with large multi-colored polka dots and a peter pan collar. It was satin-y material, which I actually thought felt cheap, but I would have bought it anyway if it had fit properly.