Sometimes you have to buy it, but if you do, post it so others don't.
Z-Library isn't really research oriented, but you could try it. I have no idea how much scientific content is on it, not why I'm there, but FMHY says it has 'educational' content just like Anna's Archive does, and I've seen textbooks on there before.
Anna’s archive includes Z-lib in its search results
Well, shit.
Try WOSONHJ or the Nexus/STC Telegram group. There's also /r/scholar.
The nexus bot was removed because of copyright and the website and IPFS don't work, they are stuck on searching.
Okay, so keep looking elsewhere? Not sure what I'm supposed to do about it.
Scihub if its before the last few years. Otherwise email authors and/or post a link on a science forum asking if anyone has a pdf to share.
This is the best answer. Just ask the author for a copy. They'll often time have no problem sending it to you for free.
Anna's Archive has a full mirror of SciHub called SciDB