Have a look at a real oval and see just how many arcs there really are.
Should be easy to do with CNC, but manually a long and painful job to machine.
When I do them (especially if there are many to do) I file up a thin ali blank to the shape that is required and use that to scribe around and mark the metal which has previously been 'blued'.
If you have already drilled and made your blanks, you can put them on a mandrel, stuck together with superglue then horror of horrors, file them to shape by hand en mass. Yes it really can be done, and I promise you, your arms won't fall off at the end.
It really is very easy to do and would take much less time than it would take if manually machining them. You would most probably have to resort to a file at the end anyway, to blend things together.
John