If you belong to a M/L club, state or national association like NMLRA, it is already part of their bylaws to promote the sport. If you don't like the way things are going, or you have ideas you think would be more effective, those seem to be the places where your efforts might have the greatest impact.
If I'm at the range and someone shows an interest, I will take the time and respond. If there is a young fellow with his father, I 'always' offer to let him take a shot, with Dad's permission of course. So far, all but one has taken the shot, which translates into probably dozens. I cannot remember a single one that was not wide eyed, and grinning from ear to ear after the shot, Dad too. What impact that will have down the road is anyone's guess. I don't force feed, just a friendly gesture.
Robby