First, is this for college level research?
Second, there are a lot of online primary source data bases but the main issue you may run into is that they will not be in English. If you speak French, great. If not, your available sources are going to be much smaller in quantity. The reason I ask if this is college level is that many college libraries offer research guides to their students with links to primary source data bases on numerous topics. You may still be able to access these without being a student but you will have to track them down yourself or pay a fee to access them. Some data bases I commonly use are jstor, 19th century collections through Gale Primary sources, and Euro Docs. You can search these databases with key terms and numerous other filters. Once again, if this is college level, your instructor should have gone over this with you. If not, speak with them about finding sources as well.

Another option is to find some secondary sources on the topic you want to write about, that is books and journal articles written by scholars that study the topic. Look at the sources they are using and try to track them down yourself. Historians love footnotes so good research will be cited constantly with a ton of sources for you to examine yourself, however, this plays into the language barrier again as many of these historians may be fluent in the language and able to read it themselves without a translation.

That all being said, I can only think of a couple of books by the same author that may be a good starting point for your research:

Zamoyski, Adam, Phantom Terror: Political Paranoia and the Creation of the Modern State 1789-1848, (Basic Books: 2015).

Zamoyski, Adam, Phantom Terror: The Threat of Revolution and the Repression of Liberty 1789-1848 (William Collins: 2015).

Some other options may be to pick up some books with sources about Robespierre and other Revolutionaires to get some context. Best of luck.

Hi - we as mods have approved this thread, because while this is a homework question, it is asking for clarification or resources, rather than the answer itself, which is fine according to our rules. This policy is further explained in this Rules Roundtable thread and this META Thread.

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Additionally, while users may be able to help you out with specifics relating to your question, we also have plenty of information on /r/AskHistorians on how to find and understand good sources in general. For instance, please check out our six-part series, "Finding and Understanding Sources", which has a wealth of information that may be useful for finding and understanding information for your essay.