I see patients who often work out quite a lot but are unable to improve the appearance of their calves. These individuals are usually very fit, but have disproportionate legs. A calf implant can be put in through a small incision behind the knee -- and can give great results.
Fat grafting can be done by liposuctioning fat from another part and transplanting it into the calf--however since people with skinny calves are usually skinny everywhere, this option may not be available.
This is a pretty safe procedure that takes about 1 hour under anesthesia, and is done as an outpatient. You must try some sizers in a doctor's office to see what is a good fit for you--looks proportionate