Have you tried Magnesium at all?

I have MS and get terrible foot cramps myself, and my doctor told me to buy plain over the counter Magnesium, but not one that's mixed with other things. Beware of Magnesium 'Oxide' though or you'll end up with very loose bowel motions.

Other than that you could try Tonic water. Our's here in Australia has low dose Quinine in it, and the Quinine works really well for treating cramps. My husband gets the tablets on presription, but I don't know if that's an option for you.

Before taking either, please check that Magnesium and/or Quinine won't interfere with any other medications that you take, and is/are not contra-indicated in your medical condition.