M&S and Debenhams online have a range, but the size choices are limited. I found the Debenhams ones to be extremely small in the cups, much smaller than the size indicated. Even the picture of the model on the front page shows a bra that looks far too tight in the cups. The M&S ones are frump city, but they are ok I suppose, quite soft and smooth against the skin.
I have also bought from amoena; figleaves and simplybe have a selection; and this label does nice styles if you come within their narrow range of sizes and want something a bit more glam: about the girl.
I would recommend contacting nicola jane as a starting point.