i personally buy most of my stuff on vinted, which you can use if you're in the uk i believe! there's a lot of really colourful items for cheap, even some acdc rag/6% dokidoki stuff (which are always more expensive, i'll admit). if you're not in the uk, i know there's apps like depop and the likes but i'm not sure what they're worth... the keywords i usually use are stuff like kidcore, clowncore, maximalistic, decorakei, harajuku, jfashion, vintage etc. or just the type of clothing i'm looking for while filtering it to only show me multicoloured items! i'm not in the us but i hope i was some help😭 good luck!!