Waynesfield Raceway Park in NW Ohio runs weekly 1000cc mini sprints. Usually get between 15-25 cars.
AMSA runs in Ohio and Indiana, focused on the Cincinnati area
MMSA runs mostly in Indiana, have had a mini sprint week the past 2 years. I think there were 6-8 races in the week, was a fun time.
35 Raceway Park in southern Ohio runs weekly mini sprints, struggles to get more than 5 cars.

Your best bet would be during Indiana Sprint Week. I think this past year you could have raced like 10 times within 14 days between several organizations