How I got it: Instead of asking for users on random places or my existing contacts, I decided to start by reaching out to niche journalists and bloggers interested in productivity devices and apps.
And since the bloggers themselves could use Post or Pay (it's a commitment device for bloggers), reaching out to them seemed like a good idea. Not only their audience could find it useful, but also themselves.
And it did happen. Funnily enough, the first user was a blogger whose commitment was to write about Post or Pay itself.
Very meta!