Smart people come in all shapes and sizes. Two quick "tells" on whether they're the kind you'd like to learn something from are: 1) Bright and interested eyes, and 2) Willingness to engage.
Where do I find those "smart" people? In the checkout line of the grocery store, sitting next to me at a ballgame, serving me at a restaurant, in the foyer of the hotel, in a breakout session at a conference, etc. Pretty much anywhere. If I'm not looking for them, it's my loss.
How do I open the door to engagement? I usually ask a simple question or make an invitational comment. They'll let you know quickly whether or not they're willing to engage.
Where do I look? Everywhere.
Why do I look for smart people? To LEARN. They know something that I need to know.
By the way, the education I get from those folks is pretty much cost free. The only thing it costs me is just a smidgen of my time. And, it's well worth the education.