Mulberries are not readily available in fruit shops or markets as they are very difficult to handle and perishable because of their high water content and thin skins. They soon ferment or get moldy. Not only they are difficult to transport because of its perishable nature, they are also difficult to harvest as they ripen over an extended period of time unlike many other fruits which seem to come all at once. This is why you rarely seem them in stores. But you're most likely to find mulberries in the gardens or your neighborhood, parks, in fields, especially along the edges of open bushes and ripening in late spring and early summer. Furthermore, you can spot ripe mulberries in season from a distance because the fruits make such a mess on the ground.
As a prevention for my mulberry bush to make a mess in the backyard, I have been going around the bush and collecting the ripened berries in the last couple of days, in some ways reminiscent of a nursery rhyme I have learn as a child. Once, I have collected enough berries I will make a mulberries pie. Please stay tuned.