Oh there's A LOT honestly. From when I was on Tumblr I still keep a bunch of reference blogs for clothes and fashion (both fictional and irl), and I love looking at character design sheets from games, animation etc for ideas too, I've sorta seen enough of how the clothes work in regards to giving a certain vibe or theme to a character to know what tends to work and what doesn't as well. As... cursed as some anime might be... some of them have really good designs too and that is, again, where I started. Then it's just sort of a matter of tossing colors and clothes at a character until something clicks