Envision Invasion Eradication

The demonic commanders cannot spawn in any of the invasions, they do have specific ones. But they spawn in multiple invasions. There are 6 invasions total: Naigtal, Sangua, Val, Bonich, Cen'gar and Aurinor.

Listed in the order shown on their respective pages on Wowhead (at time of posting).

Mazgoroth - Invasion Point: Naigtal, Sangua, Val, Bonich, Cen'gar and Aurinor
Gorgoloth - Invasion Point: Naigtal, Sangua, Val, Cen'gar, Bonich and Aurinor
Dread Knight Zak'gal - Invasion Point: Naigtal, Sangua, Val, Cen'gar, Bonich and Aurinor
Fel Lord Kaz'ral - Invasion Point: Sangua, Naigtal, Val, Cen'gar, Bonich and Aurinor
Flamecaller Vazrah - Invasion Point: Naigtal, Cen'gar, Val, Bonich and Aurinor
Flameweaver Verathix - Invasion Point: Naigtal, Val, Bonich, Cen'gar and Aurinor
Harbinger Drel'nathar - Invasion Point: Naigtal, Sangua, Val, Cen'gar, Bonich and Aurinor
Dreadbringer Valus - Invasion Point: Naigtal, Sangua, Val, Cen'gar, Bonich and Aurinor
Malphazel - Invasion Point: Naigtal, Sangua, Bonich, Val, Cen'gar and Aurinor
Vogrethar the Defiled - Invasion Point: Naigtal, Val, Sangua, Can'gar, Bonich and Aurinor
Vel'thrak the Punisher - Invasion Point: Naigtal, Val, Cen'gar, Bonich and Aurinor
Flamebringer Az'rothel - Invasion Point: Naigtal, Val, Cen'gar, Bonich and Aurinor
Baldrazar - Invasion Point: Naigtal, Sangua, Val, Cen'gar, Bonich and Aurinor

In other words, the following have now been found in all six invasions:
Mazgoroth
Gorgoloth
Dread Knight Zak'gal
Fel Lord Kaz'ral
Harbinger Drel'nathar
Dreadbringer Valus
Malphazel
Vogrethar the Defiled
Baldrazar

And the remaining have been found in all invasions except Sangua:
Flamecaller Vazrah
Flameweaver Verathix
Vel'thrak the Punisher
Flamebringer Az'rothel

A tip for anyone that is missing 1 or 2 of the bosses. If you do an invasion point (that has a chance at the boss you want) and get to stage 3, if you see that it is not a boss you need, you can run out of the entrance and zone back in. You will be be put into a new scenario with another chance at getting the boss. Whenever you find the boss you need, attack and boom done. This is what I did for my last one, though took 29 tries for Vezrah to show lol.

Can confirm that the last boss in these invasions can drop legendaries.