@Rigel
Getting a real, antique enema chair is probably very hard. They were probably pretty scarce with few ever made. Also, most all of the few survivors have probably been modified or re-purposed into a bench or something similar. In years of looking at enema and douche related stuff, I've only seen one, and that one was not all original.
Also, one has to define what is meant by 'enema chair'. There are basically two designs.
One style is properly called an enema chair. The user sits on it, and water is injected to fill the bowel, then the person arises and moves to a chamber pot, commode, or toilet to release the enema. The chairs are designed to aid water retention during the fill and have a half sphere or similar device surrounding the nozzle. When the person sits on the nozzle, the ball presses against the person's anus, fully plugging the opening. When the person relaxes onto the nozzle, the ball plugs the person even more. If the person tries to expel the enema and relaxes their anal muscles, the ball plugs them further. This is very like the JBL sit-upon bags. In my experience, the effortless retention tends to relax the user and makes taking larger than usual volumes easy, especially if the solution is warm. Either an enema chair or JBL bag can easily fill a person's bowel with over 4 quarts of solution and completely clean them out.
The other style is more properly called a colonic chair. Unlike the enema chair described above, the seat area is not solid, but has an opening like a familiar toilet seat. Below the seat is a pail (or toilet). The nozzle is supported by a rigid arm and is placed so that it enters the rectum a few inches when the person sits down.
The user spreads their buttocks and sits on the nozzle and clenches their anus and starts the water flowing. The user remains seated like this for the whole session. The user keeps their anus clenched until the urge to poo is very strong, then just relaxes and the bowel contents empties into the pail. The fill and release cycle is repeated as desired. Modern versions of this kind of device are available
https://www.youtube.com/watch?v=wjl5KtMoLAc
https://www.energymedicinenewportbeach.com/sitolonic-kit/sitolonic-full-package