These modern-looking costumes can be acquired as a reward in Academy Bootcamp instance (patch 2.5). By finishing instance and quests related with it, you will get “Academy Insignia”, which later are used to buy reward you want (eternal/fabled armours/weapons/accessories, pets, consumables or costumes). These costumes cost around 4020 Insignias.

[For more info see also: Academy Bootcamp and Armours and weapons from Academy Bootcamp ]

Costume 1
Costume 2
Costume 3
Costume 4
Costume 5
Costume 6
Costume 7
Costume 8
Costume 9

Source: Costumes from Academy Bootcamp on Korean PowerWiki.