Ikea do them in several styles and sizes - not sure if they would fit any existing carcasses you have, you'd have to check. But they're very good value, even if you have to buy the carcasses as well. Opening in Dublin in July, in the meantime you'd have to go to Belfast. http://www.ikea.com/gb/en/catalog/categories/departments/bedroom/11000/
We bought the carcass from Ikea in Belfast for a large wardrobe. We already had the doors that we got secondhand from people who were changing to a dressing-room. The carcass was fantastic value and the quality is very good, as good as Sliderobes who charge a lot for the same thing.