Since the release of Overwatch, the availability of 3D printed props has been increasing. As more people play the game and gather reference images, they create models and share their work across the internet. Kevin Chang made a replica of the Oni Genji mask. He notes the parts are not to scale because he built the model in inches, but it can be calculated and adjusted based on the size you want to make. You can download the files for the Genji Oni Mask and get instructions/notes at MyMiniFactory.