The oil pressure gauge...wtf.
 

Do I even have an oil pressure gauge?

I don't see one on the dash, and the manual only mentions an idiot light.

This idiot likes gauges, and I think I want one.

Is there an aftermarket one available specifically for the Boxster?

Nope, the 986 didn't come with one. AFAIK there isn't but I'm probably wrong on that point. I do know that others have used the 996 pressure sender (two leads) when they install the 5-pod 996 cluster (which has the oil pressure gauge).

Deserion is correct. Here are instructions for adding a 996 cluster: Porsche Boxster 996 Gauge Cluster Upgrade - 986 / 987 (1997-08) - Pelican Parts Technical Article
I was able to repair a damaged cluster and use it in my car: http://986forum.com/forums/general-discussions/43017-carrera-gauge-swap.html

I have also seen folks install aftermarket gauge packages in the area used by the storage cubbyholes or CD holders in the center of the dash.