Wavy, I have read that yes you can use ACV for your malic acid source and it has more than apple juice.
But I don't know what proportion.
You can certainly buy organic apple juice or cider at the health food store. They usually have some in the fridge. Or, you can even buy it off the shelf and it's still organic and has the malic acid.
I drink one gallon in the four days leading up to the flush (including flush day).
You can also take malic acid capsules. I buy mine at Swanson Health (just google the name) and follow what it says on the label.