drawing references linkspam
This probably is already obvious to anyone not me, but: I was browsing the internet archive for books, and found that they archived some vintage mail order catalogs, which have lots of pictures and illustrations and thus are great for easy to find period references for anything from clothes to carriages, farm equipment and kitchen stuff. Not to mention that it is just kind of cool to look at mail order catalogs from 1900, 1907 or 1920. I had no idea that you could find old catalogs online, but there's all kinds of interesting scanned things with pictures available there, like I found some sort of British government guideline for protective clothing worn by female factory workers in 1917, with photos of what they were wearing.

I also found old course books on fashion drawing and costume design, which look kind of helpful for clueless and fashion-challenged people like me to figure out how clothing more complicated than t-shirts actually fits together, because when I look at pictures of older clothes I often can't figure out the pieces, and old photographs aren't the clearest either. I mean, even drawing contemporary clothing is hard.

I also found this old book on pen drawing with lots of examples for different crosshatching and other b/w inking techniques for illustrations, which I have only skimmed so far, but it looks interesting.