If you are going to spin your own handle from cork rings you don't really need to copy an existing handle. One of the advantages of making a custom rod is that it fits you. Just get an idea of where you might want the curves to transition from concave to convex and start sanding. Grab it with your hand to test the grip and keep sanding until it's just right.
A template library is a neat idea to duplicate off the shelf handles.
I've got one rod where I made the handle from burled cork that's as thick as a stand up tuna rod grip. I find that I don't have to grip it as tightly and it just fits my hand better.
Good luck and show us what you come up with.