apple juice is a fine way if you don't have problems with sugar/fructose. You can also take malic acid supplements, which should be available at your local health food store. There's also something called PhosFood that my naturpathic doctor recommended, but I never found it.

What many of us are taking is Gold Coin Grass from www.sensiblehealth.com. That is a site worth reading thoroughly! :) Some people have cured pain just by taking two tablespoons, others have had spontaneous flushes just from taking it and doing Yoga.