I had three decomposing issues of the Saturday Evening Post from 1934, so I've photographed the cartoon advertisements or illustrations in them and put them on my Flickr site (click through the link because they're not all posted here).
Among others are William Steig:
Fontaine Fox:
The now forgotten Wyncie King (who, for a Washington connection, has some papers in the Smithsonian's Archives of American Art):
Ripley's Believe It or Not:
...and other including Tony Sarg, Raeburn Van Buren and Herbert Johnson (and doesn't this cartoon still apply?)