Librarians! They aren't just moving books around on carts. They actually study how to find information for several years. They are information finding professionals. (And other stuff like organizing, presenting, preserving etc of information.)
Even if you think a random librarian won't know about your topic, they are very likely able to help you find out about it.
Libraries are one of the few places where you can just walk in (or call, or chat, or email) and ask someone for help and get it free of charge no hassle. If you aren't near a library or you don't find your local library helpful, just reach out to some other one. They don't check if you live in the place. NYPL has very generous online materials and assistance. But you can try other cities.
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