Your case is a bit curious. You have one removed, but still not sure of the size. At time of surgery, the surgeon could weigh the implant, measure the base width of the implant, or immerse the implant into a measured cylinder, where the amount of fluid displaced is the volume. If this was not done, the surgeon who took the implant out may have sent it to pathology. They may still have it, (doubtful).
That said, it is a good idea to have the old operative note from the previous surgeon. The time period that you are trying to cover is a while ago, making it more difficult. the old surgeon may have sold his practice to a younger surgeon. If you had surgery in the hospital of surgery center, they may still have the records.
Even without the old records, an experienced Board Certified Plastic Surgeon should be able to give you a good result.