I went to GrabCAD, and downloaded a 50mm fan.
With some luck, I found one where the fan blade was separated from the mount assembly.
I increased the thickness of the blades to 2mm, and shrank the center part holding the blades.
Now, I am waiting on the good folks at PreciseBits to provide the nut dimension I am using.
bottom line, if you start from scratch, it would be a long process, but if you find a model (other than STL), you can at least modify it.
Dealing with meshes in Fustion is a pain, and the GrabCad models are vector, pretty much always compatible with Fusion import (upload) feature.