In Myeongdong, Olive Young Myeongdong Town (53 Myeongdong-gil, 1F-2F) and

Central Myeongdong Town (M Plaza, 27 Myeongdong 8-gil, B1-3F) are open until 10:30 pm, fine after a work dinner. UNIX Magic Flat says 프리볼트 in its name, with 200+ reviews. Hair tools aren't liquids, so carry-on is fine; cordless ones have lithium batteries with different rules, so I left them out.