Madonna fans around the country dug deep into their pockets yesterday, handing over $ 49.95 to become the first owners of their undressed idol’s fantasies about S&M, bondage, and nude pizza eating.“What will I find? What you always find in Madonna’s music or videos or books–sex,” said Howard Silvera of New York City, clutching his Mylar-wrapped copy of “Sex.” The axiom that “Sex sells” apparently was true at book stores across Los Angeles, as well. And “everyone” was buying, according to several outlets contacted. “We’ve never seen anything like it,” said Michael Sgriccia, Waldenbooks district manager. “It’s flying out of the stores.” Sgriccia said the stores in his region had “reservation lists of hundreds of names.” At Book Soup in West Hollywood, “Sex” was selling “like hotcakes,” according to manager Camilla Denton. “It’s doing brisk business,” said Ed Conklin, the store manager at Dutton’s Books in Brentwood. “There’s no waiting in line, but we’re getting a lot of calls.” Conklin predicted he would sell out his initial shipment.