The serials were re-released on DVD a couple of years ago and should be fairly easy to find... but don't expdect too much.. they were shown to kids one chapter at a time and have cliff hangers.. so you come back the next week to see what happened. In the 30s and 40s (before my time as well) there was no television and a lot of people went to the movies on the weekends all day. You go in the afternoon and you see previews, cartoon, a chapter in a serial, another cartoon, sometimes another chapter in a serial, a news reel (news of the day/week), a b feature movie--low budget, a film short Three Stooges, Leon Errol, Edgar Kennedy, maybe another cartoon and preview and the main feature film.
I discovered the serials when I was a kid. Condensed SILENT versions were released on 8m.m. movies available to the Home market to watch on 8 m.m. home movie projectors. There were the video tapes of their day....but rather expensive and you bought them , didn't rent them.. Castle Films ws the biggest distributors.
Later there were film societies in colleges that would show movies and sometimes shorts and serials.
Adults at night could do a 4 hour or so stint with a 60 to 70 minute b movie, short, cartoon, sometimes a serial, news reel and main feature.. usually under 100 minutes.
Expensive movie theaters were 25 cents but most were 10 to fifteen cents.