Hang on, because here we go:

The Geissele APC is discontinued; probably (hopefully) not going to happen unless they redesign the trigger itself:  as designed it places the “static” trigger in an unusual position about 1/2” off from where an AR trigger would sit.

The APC9/K FCG pocket is identical to an AR-15 pocket, so any aftermarket AR trigger should fit, right?

Of course not, life isn’t that simple.  The APC’s trigger housing:

1.  walls are thicker than a normal AR lower:  standard trigger pins won’t work.

2.  FCG pocket is slightly shallower than an AR lower:  drop in triggers may not clear (i.e. drop in all the way.

That said, it has been done and Elfman is the most often mentioned (drop in) aftermarket trigger maker for the APC.