Aichi M6A1 Seiran 3D model is available on CGTrader for $79. Original author: chipbasschao. Specs: 30748 polys, 21304 verts.
STL (Stereolithography, filesize: 10 MB), OBJ (OBJ, filesize: 10 MB), 3DS (3D Studio, filesize: 10 MB), C4D (Cinema 4D, filesize: 10 MB), DAE (Collada, filesize: 10 MB), FBX (Autodesk FBX, filesize: 10 MB), LWO (Lightwave, filesize: 10 MB)