Zak said it perfectly.
And in the case of your specific thread, it fit the profile of a Counter-Strike Kid. Those of us who have been here for a while have seen the same threads a million times from CSK's who decided based on a videogame and no real-world experience with the platform that they want an MP5, Desert Eagle, or (God forbid) an AWP. Especially with the way you phrased the question, it appeared that you hadn't done any major research whatsoever. A quick search of GunBroker or the forums would have given you the information you need to either buy a real PSG-1 or comission an excellent clone.
So, a lot of people are going to be a little ornery answering a question like yours--it's nothing against you specifically, and I personally would always prefer to avoid a thread like that than post something that's borderline offtopic or out of the scope of the original question, but not everyone's like me. Some people just can't help themselves. You've probably seen a lot of threads were someone has jokingly said "buy a glock," because people used to (and unfortunately still do) recommend a Glock no matter what question the original poster asked. Then, for a while, it was "buy an XD." Now it seems like "buy an M&P" is the standard reply.
And, I don't want this to seem like I'm attacking you. It's perfectly fine to see something in a movie or a video game and want to buy it. I'm sure James Bond was responisble for a good portion of Walther's and Aston-Martin's sales back in the day
But when you come in asking a common question like that, you have to assume that people are going to think that you haven't done any research, so they're going to try and provide you with other options that may turn out to be better options. Easyg was right on that one.