Once the camera top cover has been removed, it should be easy to replace the cracked window by a piece of glass coming from a specialized shop dealing microscope glass sheets for biology labs. The cracked window is probably nothing more than a flat sheet of thin glass, either hold in place by a metallic frame and a few screws (like on the Nikon rangefinders) or glued on the hidden side of the camera topcover (Leica M manner).
Of course there is the question of the viewfinder coating but it's on the prism itself not on the outer protective window, in general.
Any competent camera repairman located in a city large enough so that he can get some microscope glass sheets and custom cut them himself using a small diamond pick glass cutter should be able to fix your camera.
