I have some information on this siren:
The siren is 12 port single toned. They are very rare to find. Yours appears to be an older model, as Ian (murrfarms) said. The sheet metal covers and horns wouldn't be hard to re-fabricate. Ian has some videos (
http://www.youtube.com/watch?v=--maqZMonTE) of a Little Giant that can give you a visual of the original housing and horns.