1. The FBI's Famous Cases & Criminals archive (fbi.gov/history/famous-cases) has detailed breakdowns of real fraud cases, Ponzi schemes, and confidence operations. The language they use is clinical and precise, which is perfect for getting the procedural details right.

2. The FTC Consumer Sentinel Network publishes annual reports on the most common fraud tactics in the US. Great for understanding how modern scams actually work and what makes people fall for them.

3. The Smithsonian's American Art Museum has a free digital collection of forgery case studies. If your character forges documents or art, this is gold.

4. Court Listener (courtlistener.com) is a free legal database where you can read actual court transcripts from fraud trials. Want to know how a real con artist talks under oath? This is where you find out.

5. The Internet Archive's collection of old newspaper crime sections. Search for "confidence man" or "swindle" in papers from the 1920s through 1960s and you'll find incredible real stories that would feel too dramatic for fiction.

Bonus: The Psychology of Fraud section on the Association for Psychological Science website has accessible articles about why people trust, how deception works cognitively, and what makes someone a convincing liar. Essential reading if you want your con artist characters to feel psychologically real.