Honest to god, I get almost all my stuff for super cheap off of the Wish app and they have tons of the style you're looking for bc quite a few of the stores there ship from Korea, Japan and China. They sell stuff in bulk so prices are wowowowow.
As for in NYC, I don't know if you've tried this but sometimes I just walk down to Soho and there will be smaller shops and they'll usually have signs out that say Warehouse Sale and I've been able to get like two full outfits for like 60 bucks
As for actual j and k fashions, I'm unsure but you could always try K-Town even though I usually just go there for food and facial masks (korean facial care stuff is craaaaaazyyy nice).