I was very impressed by the NCDS students and staff as well, even with all the advantages they have. You will never find that situation in a public school, even in the wealthier Boston suburbs - (where I'm currently student teaching) The staff just doesn't have the freedom or time to do the preparation, nor the curriculum flexibility. Your only hope might be to work with seniors the last week of school after AP exams are done, and they are fully into 'senioritis' and the staff doesn't attempt to each them anything anyways. But even then, the same staff have the other class years to get through finals.
Perhaps your best option in the city is to focus on charter schools and get to them at an earlier age. But even there, the charter schools have the flexibility, but are even more obsessed than suburban public schools in catching up academically, that I don't think they would go for O.
As for a scholastic league, suburban private schools that don't have a big athletic program might be your best bet. Find 4 or 5 with convenient access to a training terrain, provide maps and volunteer coaches for the first season, set up a dual meet schedule for mid-week and use regular NEOC/CSU events on weekends as 'invitationals'. We should sit down and come up with a list of schools to approach...
At one point my mom was interested in starting a club at Concord Academy (where she teaches now) and has taken many students orienteering over the years. I think that's a private school with a lot of potential, especially since half the student population is a rather captive audience (residing on campus). She (and her beloved dog) have had a tough year, and I guess it's almost over anyway, but I think she'd be into helping out next school year.
I've long had this pipe dream of starting a private school league in our area. There are so many, and most have big campuses that would work well for sprints and beginner courses.
But I don't have the time now, for sure, and I don't know if I'll ever have the guts/initiative. If I somehow get motivated I'll talk to you about best practices!
I've started to think about an approach that would be fairly easy on us.
Prepare informational materials, and send to schools - how-to manual for starting a team and training on or near campus. Tell them how to make a map if they need to do that. List skills for their kids to learn, and provide a common structure for each practice along the lines of Erin's lesson plans, where you learn through playing games, or the activity itself is just fun like in ARK.
Have a list of competitions that your club puts on in convenient locations that will serve as the event sites.
Create a series of park-Os, like on Sunday mornings, circulating through 4 parks in the area, for 3-4 months. (1st Sunday always Dana Park, etc.)
A little PR - get it into the papers and whatnot.