Angellist is a good place to start. Meetups are great (depending on your area), coworking spaces (Like WeWork, etc), and even conferences for your niche.

It's very unlikely that you'll personally meet the right person, but actually fairly likely that someone you meet will know the right person. So just talk about your idea with everybody who will listen, get those business cards into people's pockets and see what the universe brings your way.

You'll wanna get facetime with "connectors" (if you've read the Tipping Point, you'll know what I mean). An email intro from one of them to the right person is all you need.