This is certainly a working progress. Please feel free to download improve and edit.
This Helmet was created by 3D scanning a figurine and modifying the mesh to work on a larger scale.
You will have to scale the model up to around 1500% Of the original size to get a rough fit as a helmet.
From Scan to Model
So this model was 3D scanned by taking around 400 pictures around the Figurine. The pictures were moved over to 3DF Zephy which created a Point cloud data and Mesh file.
This file was then moved in to MeshMixer and modified further and had the body and neck removed. The latter model was then smoothed and rounded and shaped.
This file was then moved in to Blender where a thickness of 0.1mm as added.