+1 for shock absorbers... the ones that fasten in two places. I was briefly a D cup and they worked then. Reason I go to John Lewis is that they always match other shops' promotions, so it's decent value even if you *might* find a previous season's style/colour online in your size if you were lucky.
Go to a bra shop rather than a sports shop; even running shops don't tend to have a massive selection, just a couple of brands they stock. M&S have their own range so it's worth going there for the fitting and to see if they have anything suitable, but John Lewis bra department would be my recommendation for both fitting and range of different brands.