Start a new game then play missions until your end of mission event is "New Blood". Click through the event of the new insurgent joining you but do not click through so much that you leave the mission debrief screen.

Then alt+F4 and do it again, and again, and again.

You will get repeats of insurgents and some that don't come with their own individual achievements, but eventually after much quitting and restarting you will get them all.

Beyond the achievements the best thing about this is that all Insurgents will be available to be chosen at the start of your next game.