Van's Aircraft/Hartzell Prop
Special ordered the Hartzell D-4798-1P polished spinner though Van's. $1540 plus shipping. You need to reach out to Barb at Van's if you want to special order this spinner.
The spinner that Van's shows on their website for the Hartzell three bladed composite prop is the C-4582-P. The D-4798 spinner is a bit longer and I like the aesthetics better.
I have the Show Planes cowl. I haven't installed it yet, but another RV-10 next to mine at Synergy Air South has the same cowl, the same prop and the unpainted version of the the D-4798 spinner installed. It looks really nice.