From where can you get indian authored engineering/cs textbooks?

There are some such books in libgen for sure. But not most of them. There are people that I know who have all Indian authored textbooks ONLY. Where are they? Some of the books they had are these-:

  1. System simulation ds hira
  2. Big data and hadoop vk jain
  3. Big data and analytics seema acharya
    4)System Simulation, Modelling And Languages
    R. Panneerselvam, P. Senthilkumar

From where are they getting these ebooks?

They are most definitely not getting from uni access because most unis don’t keep local/indian authored textbooks that’re not very renowned.

I tried IRC, myanonymouse but these books that they had weren’t there either.
Where are those books then? I want to know really. I have exam in 1.5 weeks, if you could share these books to me it’d be great as well.