Sorry to hear you were unable to find them a home, but that's not unusual for large fish. The albino channels will likely need the cinderblock next, or a good cajun recipe. The Connecticut State record channel cat was an albino presumably released from an aquarium owner. At 29 lbs and 37 inches it could nearly eat your pacus.
My worst too big fish was a red snake head that ate a few favorite catfish including an albino channel cat given to me because it outgrew the owners 55 gal. The snakehead would swallow the fish as far as it could then simply bite through them, often leaving the head and organs to survive and need to be euthanised. I was only a teen at the time and the snakehead (20" +/-)died of my poor housekeeping.
Today it's a real pet peeve of mine to see pet stores selling animals that virtually no one can properly care for. In addition to those already discussed I'd add about any fish that typically exceeds 18" but certainly anything over 30". As you stated you were admirable and purchased larger housing, about as big as most people could fit/afford, but still it wasn't sufficient. Considering I like reptiles as well, Burmese pythons, Anacondas, Monitor Lizards, etc would also be added to my boycott list if I knew of any stores that didn't offer these animals when available.
Sorry to ramble but as you can see you hit a nerve with your story.