I am trying to book a one-stop flight CTG-EZE on January 2nd (it's very important to be on that day).

Looking at Expert Flyer, the best option in theory would be on COPA, doing CTG-PTY-EZE. Can depart CTG at 9:21am and arrive in EZE at 9:33pm.

However, these flights do not show up on ITA or Kayak because CTG-PTY apparently has no seats left. Is that correct? Not sure if I am using EF correctly, but it says (for CTG-PTY leg):

C5 J0 D0 Z0 Y0 B0 M0 H0 Q0 K0 V0 U0 S0 W0 E0 L0 T0

Ideally, I'm looking to use United miles or Delta miles (have plenty of both). However, I want to make only one connection and depart/arrive at reasonable times with short layovers.