Roundover router bit to get a large radius molding
Rough out shape using multiple rips on a table saw, then either 

1)  Sand. Create a set of concave sanding blocks by feeding a length of 2x4, on the flat, across a table saw at an angle. Choose an approximately appropriate blade diameter.  Recess will be closest to circular the closer you feed to 90 degrees, and will be an ellipse otherwise.  Cut high quality sanding belts of various grits in half and glue them into the concave recess.

2) Router.  Buy a large high speed steel router bit of any profile and grind it to shape on bench grinder.

I've done both of those.

3) Shaper. Use router like a shaper, making two passes, assuming you can find a wing bit that would cut 1/2 half the profile.

4) Lathe. Turn square stock on a lathe to your diameter, then rip the flats on a table saw. You could get at least two lengths per turning depending on the measurements.