Near Seongsu, head to Daiso Ttukseom Station (6 Achasan-ro), 10am–10pm, which

carries these. It's close to Line 2 Ttukseom Station, and stock can change. The Meonggeuli Nyanggeuli stickers are 4 sheets for ₩1,000 with 5,000 orders, rated 4.9. Ttukseom is one stop from Seongsu, so it's an easy stop after your walk.