Piracy

I really love the Tachiomi android app. You just add sources and build an endless library of comics to read right in the app and download.

There's a lot of comics on Soulseek as well

Try some of these.

Lots of manga sites out there, and other than tachiyomi there's a desktop multi-site downloaded I've used. But for western comics I use getcomics and I've never had a problem finding anything, lots of large collections.

So far getcomics.org served me well, although I don't have that much of an extensive comic library yet.