There's a gigantic set of cards, plus some smaller sets, produced by a video game historian-type guy.

https://thewalterdaycollection.com/

I got a nice little bundle of them today and they seem to have been produced on a monthly basis over a long period of time. His site provides a lot of detail, and I'm thinking this may be one massive ongoing set or sets. I'm hoping to find out if these are all giveaways at events and trade shows, and such. It doesn't seem these are for-sale cards.

The flagship set seems to be Superstars of (place year here): Video Game & Pinball Trading Cards. From what I can there's nearly 3500 different cards.

There is Science Fiction Historical Trading Cards, 177 listed on the site.

Biographical Trading Cards, with subsets like "Scientists & Inventors", and "Authors & Poets." At least 1200.

Movie History, at least 43 of them. Movie posters and lobby cards.

Comic Book History, at least 105. Features comics and artists, convention posters.

The website says all the images are public domain and the text on back is plentiful, some info being credited to Wikipedia.

How, exactly, does one obtain these cards? I am interested in some of the science fiction author ones.

Philly Card Show card #86 features Walter Day (a guest at the May 2015 show), Harris, Roxanne & Marlin feature on a Walter Day card and some cards were distributed at that May show

These seem to exist in a world of their own. No real distribution, just cards he seems to print when he can. Its odd. They are not promos, they are not pack cards, they are not factory sets. The images are all public domain and the text on the backs is often credited to Wikipedia.