This certainly goes on, but the artists they favor tend to be long-dead ones like Remington and Moreau. If modern bronze sculpture sold better, I'm sure they'd offer copies of that as well, but as it is, they stick to the tried and (not so) true. Here's a typical site:
http://worldofbronze.com/
Anyone purchasing a bronze from one of these places expecting to get "artist's originals" is not exactly a sophisticated art connoisseur...