Thrift stores are great for this.
Best place to check out is thrift stores! Sounds weird but there are great finds!
Check out aliexpress. it's a Chinese Website and all seller there are factory owner hence you will get a damm too cheap clothing. And also have offer for free shipping.
whaa i had the same issue when i got into lolita style. your best bet is to try out Ebay and etsy shops. On ebay be sure to click "price+shipping-lowest" or just check out bids. i know you said you checked these out already, but there arent really any shops that cater to this specific type of clothing i can think of off the top of my head. you could also try upscycling though: which is taking old thrift shop clothing and dying/decorating it to suit your style.