In the United States, the President has the authority to declare a commemorative event or day by proclamation. This is very rarely done; less than 150 are granted in an average year.
Until January 1995, Congress had been active in seeing that special observances were commemorated. Members of the Senate and House could introduce legislation for a special observance to commemorate people, events and other activities they thought worthy of national recognition. Because these bills took up a disproportionate amount of time on the part of senators and representatives and their staffs, when Congress met in January 1995 to review and reform its rules and procedures, it was decided to discontinue this process. However, the Senate still does issue commemorative resolutions which do not have the force of law.
Some state legislatures and governors still proclaim special days, as do mayors of cities.
How do organizations promote awareness about an event or concern that they feel deserves recognition by the public, like the special candy celebration days listed on NCA's website? Usually a company or individual connected to the candy type contacts a major calendar of events publisher - like Chase's Calendar of Events. The day is often chosen for a significant reason. For example, the day before Halloween is Candy Corn Day.