I just took another look at the categories for the Mexican 1000 rally and they do indeed have ATV classifications. Last year there were no ATVs so you probably won't have much if any competition in your class but this still would be a good intro to rally for you.
Entries are open now: https://www.norra.com/
I did it last year an had a blast. Being from the northeast part of the US I never knew how amazing the terrain in Baja really was. Seeing bits of TV coverage of the Baja 1000 doesn't do it justice, you gotta go see it for yourself.