Hiya!!
I'm not super experienced, as I've only been getting comfortable in my style for about 3 years now, but I find that buying merch from your fav bands definitely helps get your style out :3 Not only that but it supports the artist!!
I've been using Etsy for accessories-- there's a lotta independent creators/small businesses on there. It can be more pricey than fast shopping, but it's ethical and supportive!
Ebay has second hand stuff, facebook maaaybe you might find sum stuff from other alt ppl selling out old wardrobe stuff too, I follow an emo person on insta that goes thrifting then sells their stuff!!
Irl markets might also be a good spot-- I have a rlly nice pair of cross earrings with red gems in them that were handmade from this couple
That's just the suggestions I can give as a young alt person :,)
GOOD LUCK!!!!!