So, I just stumbled on this really great resource. This website contains scans of illustrations from public domain books. https://www.oldbookillustrations.com/
Well, I'm definitely pleased to have something like this at hand, although, for the few names that I know, I wish there were more than what they have. Sure, it's a generous selection already, but some of them had a lot of work, some pretty well known, that isn't on the site but could probably be considered public domain now. May be they'll get more in the future.