find a youttube video with it on - get a youtube to mp3 converter (free)
bang you then have it mp3 format. sample it - make loads of dosh and then give me 20% of your annual earnings for coming up with the idea.
the sound you are looking for is called a lickshot, made by a "lickshot box" or dub siren, these are simple synths, traditionally made as bespoke units for a (reggae) soundsystem for use in soundclashes and live performances, although now there are a few manufacturers making them for general sale
check out Tsunami Sounds' TS1 here
you can hear the desired sound starting at around 3mins,
or the Rigsmith NS1
which is also capable of producing this sound..
both manufacturers are sound. if you obtain a siren then you'll have the ability to change some parameters and come up with more original samples, record the sound at high quality and also have the box to use live.. if you don't want to buy a siren you could look into making the synth yourself either physically or virtually in reaktor for example, they aren't so complicated. i believe both sirens are derived from an existing design called the "NJD SE1" if you google for NJD SE1 schematic you may be able to find the plans.