Maybe 5 years ago, the AMA had a killer press guide that listed results since the start of AMA Motocross.
Not only did it show results for every single national, it had sections showing the win totals by rider in every class. It also had season results for every class, all the way back to the beginning.
The .pdf was like 100+ pages and it was available on the AMA site.
Alas, it has disappeared. It was a great resource and I wish the AMA had kept it around and updated it annually. Maybe somebody somewhere downloaded it.