The FORScan development team (a small group of passionate Russian and European developers) monitors forums and known piracy channels. When they discover a leaked key, they add it to their blacklist in the next online validation update.
For $12 (approximately), you can purchase a directly from the FORScan website. This key never expires and is tied to your specific PC.
Even if you find one that matches your PC (extremely unlikely), the moment the real owner updates their PC hardware or FORScan phones home, the key will be blacklisted.