You can normally look for period posters with a google search, and there are ones that you might be able to find props from various movies set around then.
Just scale them right and print on standard printer paper, give it a bit of tea or coffee to stain it somewhat, then glue it in place. Then seal it.
For graffiti, one of the more interesting ways to do that is to print it out on an inkjet on normal printer paper after mirroring it, then cover the image with modpodge (use clear drying unless you have a lot of white in the image itself), then, while it's still wet, press and smooth the paper (modpodge side to the thing you're trying to leave the graffiti on), then let it dry. Use a brush and water to remove the paper and leave the image behind to be sealed on.