Thanks Tigris and John. I did look around the house for the right size ball, but didn't have one. Then I got my 3d printer and in a few minutes I had a decent nose, so I'll go with that. I hope that doesn't disqualify me.
I know a lot of rocket models suggest using a small bead for the tip of the nose cone. I never had problems with cones, cylinders, or other geometric shapes - even petal nosecones - but the kind in this model stumped me.