I have never seen or heard of such a camera.
To separate the viewfinder from the camera would require you to have an electronic viewfinder.
All cameras with electronic viewfinders are large/heavy and they can not be separated from the camera.
I'd like to purchase an extremely light still or video camera. The best would be if it weighed from 2 to 5 ounces, and the viewfinder could be separated from the body so that I might only hold 1 to 2 ounces up to my face. (I wonder if a camera repair person could jerryrigged something.) An extremely light camera with a swivel might work. An older D-snap camera wasn't light enough for the trick. I know there are key chain cameras - a high end one might work.