I buy them at Walmart in a 3-pack box.
DampRid® Hanging Closet Freshener
The DampRid® Hanging Closet Freshener is a unique fragrant hanging dehumidifier to keep your closet free of dampness that can cause odors and mildew. Simple and easy to use, the Closet Freshener consists of two sealed compartments: the top contains calcium chloride in a one-way packet that allows moisture in; the bottom portion acts as a reservoir for the collected moisture that drains down from the top. The reservoir is see-thru so it's easy to determine when the Freshener needs to be replaced.