need help finding a dress!!

Hi guys! i'm looking for an event dress (long, fancy/sexy etc.) for an upcoming "ball". could people tell me of best/reliable sites or shops (in and around dublin) for these dress types if possible?
looking for a black or deep wine colour
and ive found a picture of one dress (facebook, a person i dont know so cant exactly ask..) that i like but no clue where to find it!: its a long, black, lace type which is halter-neck and has a cut going down the centre of the chest, not in a revealing way but it was really nice!