There was an electric one on a warehouse that went up in London of late, the neighbours would probably let you have it for free, as the fire set it off and it went on for most of the night
Probably what you want is this
replica WWII Japanese Hand Crank siren | eBay
Which I think you will find is this one
YouTube - Broadcast Yourself.
One was for sale here
wwii air raid siren for sale • FighterControl • Military Aviation Forum
You need to search for Carter sirens
Alternate with films showing their operation are these from the states
Search results for: 'Siren' - KeepshootingŪ
Can you not borrow one, must be some reenactors your way with one.