To remove the mirror, remove the bracket on top of it (2 screws), that's it. Get a new surface mirror (a normal mirror will produce douple images), 48mm x 45.5mm, thickness 1.2mm. While you wait for your new mirror, clean the housing and repair the shutter.

As a source for a new mirror, I used weidner-glas.de but I don't know if they ship internationally. It doesn't need to be a high-tech surface mirror with a reflectance of 99.995%. Anything over about 90% will do. I don't even know the reflectance of my new mirror, let alone the original reflectance of the original mirror.