Quote Originally Posted by Enkidoh View Post
Seasonal costumes are available temporarily when it's respective event rolls around at that particular time of year (like, the Santa costumes are available during the 'Starlight Celebration' at Christmas, fittingly). The next seasonal event due is the Easter event 'Hatchingtide' which should be happening in the next few weeks sometime.
They added events' gear to Calamity Salvager NPCs, although availability may be restricted to gear you have acquired before, can't really tell.