Okay okay okay okay, we need to do this with famous Summons.
Ships might be seen as being too close to Mist, but we can get the permissions of Summons in a way we can't get the permission of (say) famous Leaf ninja. They're new enough that we aren't being disrespectful to a Leaf tradition by partaking in this, and there's no established industry to disrupt.
And then, from there, we can quietly release a rulebook for battling Summons. And release new Summons every now and again. I'm sure that the board game industry would be oh-so-happy to publish our rulebooks for a moderate cut of the profits.
Originally, I wanted to do Pokemon cards but with Summons, but this? I think this is better. We just need to find some retired/crippled Earth element nin with absolutely zero sealing experience and then convince them that this technique is worth levelling. ("You'll get to interview Summons and be an important part of transcribing their history!") From there, we have a production line, and we can make children want to come to school. Good grades in your GED? Here's a guaranteed A-rank geode. Consistent attendance? B-rank. And if we stick to Leaf's Summons, it's even patriotic, to say nothing about how I'm pretty sure that the Summons will all want to be revered by Leaf's children.