There is currently no known specific use for these items, although they can be used as ammunition for the Rock-It Launcher in Fallout 3.
Baseball gloves can be found throughout the Capital and Mojave Wastelands. Specifically, they can be found in Tenpenny Tower and in many of the Vaults, in addition to schoolhouses. There are several strewn about on the baseball field at Fordham Flash Memorial Field, along with other baseball equipment. They are usually found alongside a baseball bat and baseball, as it is first found on the Lone Wanderer's desk in Vault 101. Rarely they can be found on centaurs or feral ghouls.