i'm afraid you will probably struggle now. Most shops have had their summer sales, which usual mean selling off all the summer clothes ready for the autumn/winter stock. This includes swimwear unfortunately . What about ordering online?
There were loads in Debenhams in the Metro Centre the other week, I was looking (and bought) from the bra sized type range (Freya, Fantasie, etc), so good discounts ranging from 30% to 50%. Also ordered a whole load from Figleaves (look in the Discount Codes section there is a 20% off code, think it was "compaug" it might still work). All but one of the Figleaves costumes went back but they had loads of choice and loads of stock.