You can do a Google image search for a political cartoon, but you may run into a couple problems:
People do a lousy job describing images so they can be hard to find reliably
People reproduce and repost images without proper credit given to the author/artist or original publication
And you vow to do better.
Here are some options:
Google Image Search and Google News
Enter your keywords and use the phrase 'political cartoon' as a search term. If Google Image Search yields older results, narrow down the search by entering the year you're interested in finding images from. Click Visit Page button to the right of your image to see what website is publishing the political cartoon (note: this may not be the author or original publisher)