It need to be unfermented apple cider for those of you who live where it has alcohol in it and IS fermented.
www.bulkfoods.com sells the malic acid as well as www.nuts.com both of which are USA based companies. I have no idea if they ship out of the USA or not. www.nuts.com is very good to do business with. 1 teaspoon of malic acid in distilled water will do it, or you could put it in juice. It will certainly taste better in juice. Mot all fruit has malic acid, but apple cider has the most. You could add it to any juice.