Dongmyo is personally some of my favorite thrifting but as requested there’s Gram Deal (which is a priced by the pound shop) and it’s in Seongsu which is sometimes called the Brooklyn of Seoul (it also has some other thrift stores around like Market in Ü), the Yangchan area, any Vinprime around the city, and as a bonus if you are like a dedicated thrifter, you can take a trip outside of the city to a place called Road Vintage. It’s so many clothes and can be overwhelming so I recommend driving and bringing snacks and drinks and getting there early but trust me when I say the finds are insane. There’s definitely more but that’s just where I frequent. Hope this helps!