Just run a search on the web, many online retailers sell Amazonian fish, I've found pimas for sale without trying...
Well, today i had an expeiriance similar to yours. One of my large plecos(named scalez, and 13'' long) got stuck in a rock and died
Because i was away, i was unaware he died. Most of the other fish in the tank died(including a 12'' pleco, a tilapia, my beloved 9'' show jack dempsey
and her fry, and some other assorted cichlids. The only fish that survived were an oscar, a convict and my 17'' common pleco.
The water levels were OK before it happened(now they're terrible from all the dead fish. I'm pretty sure this is what happened because i found the one pleco in a rock and because the water levels were great. I know you had a time in your tank when half of the large fish died.