Some items, such as the apparel that showed up in stores at the end of October/beginning of November will be sold out or in limited sizes/quantities by the end of the holiday season, but many, many, many ornaments and decorations are available all year round. There are Christmas stores in the MK in Liberty Square, in DHS across from the Muppets attraction, in the Germany Pavilion in Epcot and the biggest store - Once Upon a Christmas - in Disney Springs. Also the larger gift shops such as the Emporium, Mouse Gear and the World of Disney have an ornament section.