Cramps in the legs is a common problem associated with diabetes mellitus. It is sometimes due to imbalance of electrolytes in the blood. I presume your father is attending a diabetic clinic where they will check him for this. Sometimes, quinine sulphate is given for these cramps, if there is no contraindication for prescribing quinine. Perhaps you would see your doctor and discuss this with him. If he/she considers it appropriate then they will give a prescription for quinine sulphate.