I find this extremely odd! I would think there would be a large market for beautiful cast stone things. Instead, there is (apparently) an extraordinary market for concrete frogs.
I figured that in the era of 3D printing and widespread 3D models[1], it might be fairly inexpensive to make my own mold and pour my own casts, even if I do destructive casting techniques. Here again I was disappointed: To order a 3D plastic print from a site like ShapeWays came out to over $1300 for something fairly small. So that's off the table, too.
I expected more democratization of ornament than there really has been, given the tech today. It's surprising to me that no one is trying to make silicone molds available of famous statues, generally, but I guess there's just no interest or no perceived demand. Or maybe there is a big market, and I've missed it, because I was not searching for silicone molds of frogs.
[1] For instance, The British Museum has a sketchfab with free models: https://sketchfab.com/britishmuseum