The fact that the tubing can move inside the fitting is a good sign. That means the fitting may not be compressed too much to be reused. It depends on the tightness of the nut to seal by compressing the front end of the fitting on to the tubing. It should at least turn on the tubing if you pull it off.
The captive ferrule might be available at a plumbing shop, but I've only seen them on cars. I used to work in plumbing years ago. That McMaster Carr link I posted above might be easier than running all over town trying to find one. I'd pull the tube off and see if the fitting will slip over a new piece of tubing. You may get lucky. (You need some of that right now)
