In the United States, the only option for patients looking for larger breasts implants, (greater than 800 cc) are overfilled saline filled implants. You may find the attached link, dedicated to larger breast augmentation outcomes, helpful to you. Best wishes.
I have not found any of the three companies willing to make extra large silicone implants but the large salines can be overfilled to almost double, I would not really recommend something like that though