Xpan Diopter

Over the course of the day carrying around the Xpan, the normal diopter fell off the camera and is presumably on the beach somewhere. It was pretty loose when I got it and I didn't think to secure it better to the camera :/ Where would be the best place to get a new one? Is it ok to use it without one? The rangefinder patch doesn't seem as contrasty without it. Any help would be appreciated--I really enjoy shooting with this camera.