Since you only get Harrison Jones when the achievement is rewarded, and with the achievement being warband-bound now, that means you are awarded the achievement the moment you log in the character for the first time. Yet you can’t already have a garrison built the moment you log in, so there is no where to drop Harrison Jones off into. Once you build it, you are too late and there is no way to get another chance at getting him.
This means if you didn’t already have a garrison built on that character before warbands came out, you can no longer get Harrison Jones as a follower at all.