Kobo store, Google Play Books, and various other places (here in Sweden for example we have Bokus and Adlibris) have Epub downloads. Usually with Adobe Digital Editions DRM (which you can get rid of pretty easily with DeDRM, or alternatively Kobo tablets support Digital Editions), but some books are sold DRM free, or with LCP DRM which I don’t have experience with. Something I’ve noticed at least on Bokus is that many books in Swedish are sold as DRM free Epubs with watermarks, even if they’re translated from an English version which is sold with DRM on the same store, though that’s probably not relevant for people in other regions.

Baen library has drm free books one could buy.