There are multiple references to this species being caught in several counties in south Florida. Is it possible that this fish is currently being farmed as a food fish there? See
http://www.sms.si.edu/irlspec/Sarotherodon_melanotheron.htm for some cool info on where there are to be found in Florida. Not much practical value, but fun reading!
I would recommend contacting your local agriculture board (tilapia being a major food fish) if you are unsuccessful finding a hobby importer.
EDIT: Frighteningly, a drainage into the Mississippi River down here was recently rotenoned after discovering tilapia reproducing in it. I wonder if Acestrorhynchus knows what species it was determined to be ...