There is no simple answer to the question of "what are the largest breast implants available?" Generally speaking, saline implants are available in a wide range of sizes ranging from 120cc-850cc. This refers to the amount of saline which is used to fill the implant. The patient and surgeon will typically work together to determine a size which would be most appropriate for the patient's size and structure. Implants which fall within the commercial range of 120cc-850cc are fairly easy to obtain, but it is possible to obtain implants which are even larger in size.
Patients who wish to have implants that are larger than the average size may wish to have custom implants made. Not all surgeons will be willing to perform a breast augmentation procedure involving custom implants so selecting a surgeon might be more difficult. Additionally, the procedure might be somewhat riskier and the fee for the procedure will likely be higher than those involving commercially available implants.