AFTER three seasons, “Mad Men,” the television series about advertising in the 1960s, has attained a level of popular-culture cachet. There have been magazine cover articles, calendars and an episode of “The Oprah Winfrey Show” all devoted to it, spoofs on “The Simpsons” and “Saturday Night Live,” and even a “Mad Men” category on “Jeopardy.” Soon, the show will enter a realm of the pop-culture pantheon that its creator, Matthew Weiner, says has surprised even him: Mattel plans to bring out versions of Barbie and Ken styled after four “Mad Men” characters.