Do such websites to legally acquire e-pub books even exist? I wasn't able to find one. Happy to pay for those as much as for physical copies.
I am interested in history and politics; my first target is 0199797455, assuming I can find where to buy it.
There are endless websites that sell ebooks (ePub is only one format, you can easily switch between formats if you need), just google the name+ebook or epub
Many offer such things. Your local library may surprise you as well.