A specialst book store or lending library or archive in hard to find new and seconhand books. For some subjects, amazon and its secondhand book site Abe books (?) sucks if you delve into narrow neiches. They are enthuaists out there who crave a book which will teach them something. These books are published in areas which may not be as commercial as they once were.

The neiches are small. One for example is model engineering and related subjects. Books with plans, drawings etc. Construction methods.