The meatballs can be refrigerated for up to 1 day or frozen for up to 1 week.
The yellow sour fruits are not sold here, but Middle Eastern groceries sell pomegranate syrup, also called pomegranate molasses, made from juice of the sour variety cooked down with a little suger. Look for Cortas brand pomegranate molasses from Lebanon. In recipes calling for sour pomegranate juice, dilute 1 tablespoon of pomegranate syrup in 1 cup of warm water. Alternatively, you can use sweet pomegranate juice, soured with 1 tablespoon of strained fresh lemon or lime juice per cup of pomegranate juice.