I don't suffer very often - but Arcoxia (a POM) seems to sort it out when I do - not instant relief, more a gradual easing, but the main thing is it stops it recurring.
I get cramps in my legs at night in bed, I feel the pressure building in the muscle and if I'm quick I turn over onto my facewith my feet and shins overhanging the bed-end. It works for me. If I'm asleep though I miss the onset and am woken by the sudden snatching of the muscles, then the only cure is hobbling around the bedroom. The GP says its circulation and that I should have a drink of water before retiring. He doesn't understand when I tell him I don't retire for another 6 months !! Nightly Quinine tablets sometimes help but not guaranteed. You've got my sympathy.
I suffer sometimes, maybe after walking loads, and a friend suffers really bad,think she has tried most brands, but will tell her about the ones from the healthshop that woofgang suggested