spherical garden ornament/fountain

We have a meandering dry stream bed, placed to help drain a damp area. The end of it just stops in the lawn, and it needs a terminal or a visual punctuation mark. I'd like a sphere, about 20 or 24 inches in diameter. (The red spheres used as bollards in front of our local Target store are actually pretty terrific.) My husband wants it to be a fountain. I've looked all over the Web and at several garden centers. There are several spherical fountains with water coming out the top, but I've seen none larger than 16 inches. Would casting one out of hypertufa really work? We'd need a catch basin and a pump as well, and I'd rather buy the whole setup if possible. Ideas welcome. Thanks from Indiana.