I looked at some photos on the Internet and there is definitely a web structure joining the spokes on each end. I think the way it all blends together will make it difficult for NURBs modeling - perhaps Sub D is the way to go on this one.

I attempted to make an approximation by creating filler pieces to go between the spokes. Maybe with some additional effort the filler pieces can be sized correctly and made such that they blend into the spokes more gracefully.

Ed Ferguson