I think you are right about the denver aquarium having some. When I first saw them I couldnt believe that they would be platinium but maybe they are. They did look like it. The only reason I didnt think so was because the denver aquarium doesnt really have anything that rare or cool, lol.
Denver only had one I thought? It's Pie Bald but it's thought that it's a damaged platinum. And yeah since they're farm bred on almost every continent I bet there are alot and will become even more available.
More. You have to take into account the numbers that are produced in Australian Barramundi farms. At least 15 per year. Then there is piebald which is even more common!