If I understand correctly, if you had a variable that represented the days (1-365), you could have a common event that set the variable = to the day of the year (i.e. January 5th = 5, December 25 = 359 etc). Then you could also have that common event check to see if the variable = the number corresponding to the date of Halloween, Christmas, etc. And then if the variable does = the number for Halloween, then you can have whatever you want happen after that.
Here is an example for Christmas
Control variable [day of the year] +1 #obviously upon a new year, you will need to set this variable = 0
Conditional Branch: variable [day of year] = 359
Text: Merry Christmas! #put whatever you want to happen on Christmas here
Else
(empty)
Branch End
You can just keep adding conditional branches for whatever day of the year you want, and can add 1 to the variable however you want. This would only work for an in game calendar, and honestly having a special even happen one a specific day in the real world might be kind of worthless? Using an in game calendar would be much more useful, I believe. I hope this helps.