I've been away for a while and have only just caught this one.
I suffered indescribably bad calf and foot cramps in both legs for a good few years and it nearly drove me insane. GP was no help at all and in the process of sorting it out myself I tried all of the suggestions above, and a damn sight more, to no avail. About three years ago I had a knee replacement and mentioned the problem to my orthopaedic surgeon, who promptly wrote me a prescription for 200mg tablets of Quinine Sulphate, take one about half an hour before bed for about a week, and thereafter keep them by the bedside and if you awaken with the first signs take one immediately with a glass of water.
That regime has worked so well for me that I've just been to the bedside to be sure of the tablet strength and noticed that they expired over a year ago........'nuff said, in my book. I still get the odd attack, but swallow one of these as above and it's gone.
You'd need to drink and awful lot of the best, purest tonic water to achieve that dosage, but that's what it takes. Your GP should prescribe immediately and without fuss, mine did and she's a ......well, I'll not go there.
A complete and radical life-changer for me, give it a try