Where can you find citron to buy for baking?

You cannot buy citron for baking. Citron is a type of citrus fruit with an incredibly thick peel and little pulp, making it inedible unprocessed. To make citron into the candied fruit often used for baking, it is soaked for extended periods in limewater, repeatedly boiled and discarded until it is soft enough to cook through with sugar syrup, then drained, sliced and cooked again in the syrup.

Many baking recipes call for Citron because it used to be an easier ingredient to find. These days, however, it is almost extinct. Instead of citron, bakers will often substitute candied lemon or orange peel, or even diced, dried tropical fruits like golden raisins, dates or papaya.