I'm pretty sure that if your FSX installed correctly, the HornetFCS.dll should be in the \FSX\Gauges folder. You might look there.
The v16.1 Hornet has an updated HornetFCS.dll file included, IIRC. Should be in the Panel.fleet and/or the panel.BA folder, subfolders of the Base folder. One or both, I think (although very rarely).
I have been wrong before, though. I KNOW the v16.1 has a new HornetFCS.dll, but I can't swear to the rest.
Pat☺