Finding and adding the caffeine is the easy part. You'll probably have more trouble obtaining Coke's crucial flavoring ingredient: cassia oil. I was hoping to leave such a hard-to-get ingredient out of this recipe, but I found it impossible. The unique flavor of the Coke absolutely requires the inclusion of this Vietnamese cinnamon oil (usually sold for aromatherapy), but only a very small amount. You'll find the cassia oil in a health food store (I used the brand Oshadhi), along with the lemon oil and orange oil. The yield of this recipe had to be cranked up to 44 10-ounce servings since these oils are so strong—just one drop is all you'll need. Find them in bottles that allow you to measure exactly one drop if you can. If the oils don't come in such a bottle, buy eyedroppers at a drug store. Before you leave the health food store, don't forget the citric acid.