You say Hugh Hefner once cited the wife-spanking stories in men's magazines as part of what convinced him to launch "Playboy."
I don't doubt it, but if it's so, it seems strange that "Playboy" has never had much to do with spankings. Maybe Hefner and his advisers just wanted to keep an arm's length away from the subject, for whatever reason.
With the exception of a few (VERY few) "Wicked Wanda" cartoons and some single panel cartoons, I don't recall seeing ANY spanking references in Playboy mag. If it began in 1955 and that was 47 years ago, even one spanking ref a year would have yielded 47 spanking references... and there haven't been anywhere near that many.