How do I get the Girdle of Masculinity/Femininity in Baldur's Gate 2?
There is no way to legitimately acquire the Girdle of Masculinity/Femininty in Baldur's Gate 2. It isn't available in game, and most items cannot be imported as the start of Shadows of Amn takes your inventory.
It is still available in the game files, so either spawning it with console commands (BELT05) or a save game editor such as EEKeeper can add it to your game.