The search page on usfirst.org (
http://www.usfirst.org/whats-going-on) has some inconsistencies, teams that never competitive, things like that.
Navid Shafta of GameSense/1983 has this spreadsheet up that seems to have more accurate numbers:
https://docs.google.com/spreadsheets...H_E/edit#gid=0
MI was 10.22% of FRC in 2014, having 277 of 2710 teams. This would be 61 spots with a 600 team championship.