Here are the lists of natural organic acids and their sources:
Acetic acid is found in vinegar.
Malic acid is found in apples.
Tartaric acid is found in tamarind.
Lactic acid is found in milk.
Citric acid is found in lemons.
Ascorbic acid is found in tomatoes.
Tartaric acid is found in grapes.
Uric acid is found in urea.