Good morning @Raichu,
Some of the enemies of Ultima are now dropping Summer Event Items instead of their normal drops.
These certain enemies will drop it for a certain I.D. Only.
Difficulty also plays a part in the equation.
You do not need to start a quest to do it, but it is recommended so you can get the mob of enemie(s) that drops the item you are hunting.
TheIronSheik has the current drop chart running and you can reference his post to see what drops are confirmed this year and previous years.
Hope this helps