There's a neighborhood in Tokyo called Jinbōchō, which built an entire town out of different specialist second-hand book shops. If you ever need a specific book on a specific thing, you bet you can find it there. It's pretty sweet.

And to ride on Jimbocho/international reference, they have the same in Manila, Philippines in Recto, which is a university area, tons of english university text books, around 100-200 pesos, "international editions."

Jimbocho has limited English text.

Now Hong Kong, Quarry Bay Street has a few but they're all on south island I see and accessible via the metro.

I'm fortunate enough to have that experience. I also thought there were many specialized districts. The few towns I visited all had a very sophisticated electronics district that included ancient machines, simple home A/V switching boxes and cutting edge parts.