Ironically, I've found many of the publishers will sell DRM-free ebooks. The biggest problem I've found is books out of print but still in copyright, since we have absurdly long copyright lengths today.

The "ebook shops" are the worst. Amazon & Apple have their DRM'd copies, and Kobo may be even worse.

Everything published by Tor I believe, plus, of course, everything on Gutenberg

[Edit: tor books, not the other tor. Although presumably everything is there regardless of legal status]

We keep trying to push publishers to allow us to sell their ebooks DRM-free, it really is a win-win. Less customer support for us, more sales for them, no vendor lock-in for the customer. We offer completely DRM-free or watermarked content: https://www.ebooks.com/drm-free/. I wish every publisher would embrace it.

Interestingly, all German language e-books have been DRM free for a couple of years now. I have no idea how that happened, but at one point, all major publishers have pivoted from mandatory DRM to DRM-free (but watermarked) ePubs.

The notable exception is Amazon: Kindle books are almost always DRMed from the same publishers.

Incidentally, O'Reilly links people to ebooks.com for one-off DRM-free purchases of their technical books.

I recently bought these two (in DRM-free PDF and EPUB), mostly-happily paying twice what I'd have to for paperback or being locked to a jerky-reader:

* https://www.ebooks.com/en-us/book/210313783/programming-rust... ($60; for experienced systems programmers, this seems better than the free official book)

* https://www.ebooks.com/en-us/book/209970024/software-enginee... ($51; for front-loading Googliness)

They're on IRCHighWay.