"a few years before Walkmans started appearing at the Sales"

Creative Commons AttributionWalkman - Credit: FaceMePLS
This reference to the Walkman, the portable cassette player which first appeared in 1979 and grew in popularity throughout the 1980s, helps identify the timeframe in which Never Let Me Go is set.  The Walkman was made obsolete, first by CD players and then MP3 players.