Your nephew Johnny will kill for real if he doesn’t get his hands on the latest in genocidal entertainment for his PlayStation. Being the dutiful aunt or uncle that you are (which, of course, gives you the freedom to buy the kind of electronic candy that Mom and Dad refuse to shell out for), it’s your job to save the day. But where does one find Duke Nukem (or whatever) and its ilk? Theresa Duncan, Manhattan-based creator of wildly popular games like Chop Suey, says that she’s more than willing to fight her way through the crowds of Times Square to peruse the “excellent selection” at the Virgin Megastore (1540 Broadway, at 45th Street; 921-1020), which boasts more than 1,600 game titles in stock. Just don’t tell Li’l Johnny about it.