When you are on Pinterest you sometimes find a great board. And my advice would be to also see who these people are following themselves. But anyway, apart from that, here are some great people on Pinterest who have gathered lovely boards and research images, and I am specifically looking at millinery and headdresses, and so inevitably also interested in fashion and costume.
Judith M millinery supply
A selection of millinery and headwear boards put together by somebody who clearly has a genuine interest in millinery and isn’t just in it to sell materials. One of her boards is about carving hat blocks, another about crin, another about veiling, another about cut and sewn hats plus much more.