anyone have this kind of cap bolt .ipt or step file?
That literally looks like a chunk of plastic molded over a 10-24 (guessing) bolt/stud.
Give some dimensions, and how you plan to recreate it. It is a 10 minute CAD project reproduce. A photo of the underside (where the threads meet the plastic) will be great too.
It looks like you have a spare, so casting more is a good project, but might take more time/energy/supplies than the project warrants.
I made a similar "knob" for a piece of equipment a while back: Replacement Knob
It is the wrong shape, but it could work in a pinch.
The library has ~500 "knobs" but there is no telling if they are the right size: https://grabcad.com/library?page=1&time=all_time&sort=recent&query=knob