Sine this is in the post prod section, I'll assume the video has already been shot.
Since you can't find any photos that work you will have have to make something. If you go the physical route, get a clear piece of plastic or glass. Lay it on a black cloth or black paper. Please be careful and use eye and hand protection. Then hit it with a hammer. Gently. Try to get a pattern that looks like what you want.
From there you should be able to take a photo (flash off) and comp the photo to your footage.
You may also consider looking in a junkyard/scrap yard to see if they have any broken windshields you could photograph.
Otherwise, you can draw the crack pattern. Paper or digitally. Then clean it up and composite with your video.
If you haven't shot the video yet, look for some decals online like ray said. You could go to a junk yard and see if you can find a car with broken windshield. Then shoot the close up/through the window shots there. Worst case you can rent a car with the insurance option and just break the windshield or break the windshield and pay the few hundred buck to have it replaced.
