I have the same problem, and don't like the way I feel when I drink a lot of apple juice.
I got Malic Acid in the form of Magnesiun Malate at the health food store (they had to order it for me). The kind I got is from NOW Foods,
1000 mg, cost about $ 12 for 100 tabs.
Much easier to take prior to the LF.
Apple Cider Vinegar is good (I take 1tsp, 2Xdaily in a detox drink).
Lecithin is also GREAT for softening the stones.
Eating green apples (can puree them in a blender with a little water and lemon juice)also is helpful.