Heroes 6 - Discussion

Hello, I played Heroes 6 a bit. I haven't played any of the previous installments before. They say the earlier games are even more interesting. I don't want to buy pirated copies because they often have cut graphics and sound. Where and how can I find a legitimate copy so I can play properly? Overall, the game is worth playing. It's just a shame that the gameplay is tedious and somewhat resembles managing accounting.