The offer in the Club Superstore allows fans buying an adult home shirt for £30 to pick up an away one for just £10.
Shirts for children and youths have also been reduced in price to £15.
Spireites director Ashley Carson said: "We want to see more fans wearing Chesterfield shirts. Over two thousand fans will be travelling to the match at Rotherham later this month and it would be great to see many of them wearing either the home or away shirt. Let's make it a sea of blue and gold at the New York Stadium!"