These are the only 3 years that the United States Mint issued what they called Special Mint Sets. These were higher quality sets ( Prooflike) than the sets issued before or after. There were no Proof sets issued in these years as there have been in years prior or since.
$12 each or $30 for all 3 sets
If there are other date sets that you are looking for, I can get those for you as well.