when i first heard this, and went throught the presets i thought wow! The sounds that come out of it, are kinda evil and harsh sounding. The thing is, once you get into it, it seems extemely limited. The sounds I got out of it, sounded similar to the presets supplied (and there wasnt that many), and within a few months id gone completly off it. It eats up your CPU too. It has got a distinctive sound, and would probably work well in some techno tune, but unless thats your sort of music, i wouldnt put this high on my recomendation list.
You won't find it anywhere... given that it was not free. All the copies you will find (except in warez sites but it's not at all my cup of tea) are locked copies used as a limited demo as long as you don' register.
Here is the Wayback Machine copy of the registration page of Mercury-1: