This is a new one on me...I own an S200 and to my knowledge its not based on a pistol at all, but a redesign of an existing CZ/BRNO CO2 10m target rifle.
A short extract taken from here : http://www.pyramydair.com/blog/2009/...er-part-1.html
A short history
The S200 is descended from the Tau 200 CO2 target rifle. I watched the development, and here's how it happened. During the 1990s, some American field target shooters wondered if the Tau 200 could be converted to air to compete with the FWB P70s and other 10-meter rifles that were doing so well. A couple of them converted their rifles with good results. They communicated this over the internet and soon there were UK shooters doing the same. Air Arms, a forward-thinking airgun maker, decided to go straight to the source and have the factory convert the guns to air for them. A new product was born.
Although I believe there was a rumour many years ago of AA developing a pistol based on the S200 but as far as I know it never amounted to anything.