Had to run outside real quick and take these pictures before it got too dark.
As you can see, my neighbor has a belly tank that he plans on building up. As you can also see by the dogs in the pictures, he's serious about keeping it. He won't sell it to me or even reveal his source, but he says that they're still out there for sale. You just have to hunt hard and long to find them. According to him, it took him 4 years to find this one and convince the previous owner to sell it to him.
Good luck in your search.