Stone sinks are difficult to find, and they are expensive to buy when you track one down, but the old porcelain models are more readily available at not such extortionate prices. It is then quite easy to convert one into a good replica of a stone sink, by cleaning it, coating it with a contact bonding adhesive, and then applying a roughened layer of cement, sand, and peat, mixed together with water. The mixture should only take a few hours to dry thoroughly.
Once filled with soil and rocks, the sink will be immensely heavy, so place it in its final home while it is still empty. Even empty, it will be very heavy.