Try a tutoring war? I remember this idea from somewhere, where a higher ranked duelist would teach a younger duelist in order to have them join a tournament. Basically a sponsorship.
In the version we'd be interested in, possibly a system where us Yellows try to pick and teach a Red until a certain date. Then, on the due date, the Reds that the selected Yellows taught would go in a tournament, and whoever's Red gets a reward, with that Yellow getting a reward as well. Your choice on the rewards.