Have you searched on the clker website? They have a lot of free svgs that can be altered and used in SCAL. The SF bridge would be very detailed and probably very difficult to try to trace and cut out but you might have some luck doing a trace on skylines from photos.
You could also google it. San Fransisco silhouette and then change your view to images. Who knows something might come up. I use that search all the time ________ silhouette and the images are very easy to trace.