Figure someone is going to make use of this. NY Times has an article on police sirens and includes a selection of them which look available for download including "the rumbler" although in not particularly high fidelity
http://www.nytimes.com/2007/06/14/nyregion/15siren_sounds.html
http://www.nytimes.com/2007/06/14/nyregion/15siren_sounds.html