Considering that Instant3D software is now part of SolidWorks, it may be possible that you can import .e3d (Instant3D files) to SolidWorks and use the data in projects or even export them, or at least some of the parts to CAD exchange formats, for example 3MF format.
The only other viable alternative for e3d to 3mf conversion would be to get access to some older versions of Instant3D.