This is an important question. If you do not know where to go to get scholarly articles on what you are writing, then it can be challenging. Luckily, there are many places where you can go to get articles. With that said, it is probably best to define what a critical article is. A critical article is something that a scholar has written about your topic. So, if you are writing on the collapse of the Roman Republic, critical articles are works by other scholars on that topic.
There are a few places where you can go to get these articles. First, it is good to start with a few important books on your topic. Go to the bibliography and there will be many articles on that topic. You will not be able to read them all! Second, there are many online databases of journals, like JSTOR. If your school has a subscription, you will be able to search through it by key terms. This will generate numerous articles as well.. Happy hunting.
I purchased an enotes account specifically because it contained critical articles. Such as "Our Town as Allegory" by Donald Haberman. Now I cannot find any of the critical articles that I paid to view. Including Haberman's article. I log in and look up Haberman specifically but when I click on his article I am brought to a different page.