Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
That manufactured item sure is a wimpy re-creation.
Sorry, I do not know about a clay that does not need to be fired.
How about carving it out of Styrofoam then covering it with mortar and concrete coloring material? This can be aquarium safe, though the concrete does leach minerals for a while, raising the pH and making the water harder .
How about buying the funny looking one and painting it? I'll bet Krylon for plastic would work on it. Get a couple of shades of grey and flat black, maybe a dark brown...