if you ever see a well preserved Pacemaker Crown or Speed that is near factory fresh as possible it will be Black with a sheen close to flat but with a little more gloss than flat but not much.
Trying to match an existing finish is another topic all together.
From my hardware store days the wrinkle finish is achieved by adding extra (fast evaporating?) solvent to the paint.
I use flat black on the inside of Graflex/Graphic bodies I repair and Rust-oleum satin black for exterior touch up. The Graflex Corp. original is somewhere between the two.

The Pacemaker Graflok Back frame is Magnesium.