Tuning Are the Air Arms TX 200 MkII & MkIII Stocks interchangeable?

That's a good question. PA sells the replacement stock for MK3 and HC as same application with description stating for TX200 (doesn't state anything else). I would call them or ask the online helper pop up guy. Better yet email Air Arms UK. Straight from the horse's mouth. See if Bill Sanders is still there (extremely nice guy to chat with over the phone).