It was very hard to find these comics back then - there was no internet, and you had to find a comic book store that carried them. Most comic book stores liked typical superheroes and these comics were far from that.
Later on I started to understand that there was a bunch of writers with similar, experimental styles including of course Robert Crumb, a man with strange tastes in women and a singular weirdness. The biography "Crumb" is definitely worth watching, especially when you meet his two brothers who are even nuttier. Williams, who drew the original "App*tite for Destruction" cover for Guns' N R*ses (which was banned and replaced with the new cover you see today) is also part of this group.
This box set of all the Zap Comix is available for $350 on Amazon. I am trying to get rid of lots of my books but I may have to get this in physical form.