Answer: "one leg at a time".
John does a lot of outreach, public presentations in St. Louis. I took a slightly different approach and published a few articles in our local newspaper. My first year, I garnered 19 people that were interested in hosting purple martins and / or growing their current colony.
If people are interested in helping other people, you have to let them know that you're a) there and b) available. They're not just going to trip over your site and come ask you.
I now have 72 people on my email list and reading my blog. I do a couple of site visits every year, but mostly, the 72 people I have on my list are enough for me to handle during the season. Surprisingly, even without reaching out via our local newspaper anymore, I still pick up 3 or 4 new people every year.
John Barrow used to tell the story about a child walking along the beach, tossing starfish back into the ocean that had washed ashore. Someone asked the child if he really thought a few starfish mattered, given the huge numbers of starfish on the beach. The child, tossing another starfish in the water said, "it mattered to that one".
That's my motto ...even if I change only one or 2 landlord's minds and get them setup, that's one more that matters now and will host my lovely purple martin SYs next year. You would be surprised at the numbers of opportunities out there available to you - platforms from which you can share your passion. To me - it's more about sharing that and getting these other colonies setup than growing my own colony anymore.
John, I think THAT is where the future of the purple martins is.