Just like the previous post says,they are used in conveyor belts.I have never seen one, much less worked on one.
I understand they make them up to 50 hp or more.
Try these links and I hope you find your answers.
Southwest Electric in Oklahoma City repairs such a motor, for the oil industry, where the rotor becomes stationary, and the stator rotates. You might contact them and get the name of the manufacturer.
The application is a scientific toy. I need to move an object in a circular orbit. At the center of the orbit is a shaft. The shaft is not fixed. It moves and its orientation changes with time. So I need a motor that I can "fix" on the shaft to create the obrital motion.
Dimensions are fairly small as it is a toy. The shaft diameter could vary from 0.25 inch to .50 inch.
How about an outer rotor brushless DC motor? There are some with hollow cores (for automotive fuel pump applications and the like), or you could make a custom shaft that would fit the other pieces of your application.
There are on the market what are known as external-rotor type fan motors, maybe one of these will satisfy your requirements. The major manufacture are a German Company called Ziehl-Abegg AG. Try a web search quoting "External rotor".