They are usually pretty easy to find at the Walmarts in my area, but on the one or two times they were sold out by me, I found them at a comic shop in the area at a slight mark up. Or eBay speculators.

They were supposed to be accessible to casual readers and were going for the most general status quo's possible. Tom King said all you needed to know to read his Superman was the basics. Even Bendis' Batman which is loosely set in the present continuity is pretty generic. The new Flash one has an Iris West that's african american like Candace Patton to probably make it accessible to fans of the show. Of course King then went with "Anxiety Attack Superman" for the last issue because that's definitely a story to pull in new casual readers.