The most obvious place to gather wild yeasts consistently to me is on the surface of fresh picked fruit. Get a few non-waxed apples (i.e. not the ones in the typical grocery store), mash 'em up, add some water and you'll get a yeast feast going.
That is basically what wild-fermented cider is and I've got a batch of fresh-pressed cider that I'm letting ferment using the wild yeast from the apples. I'm planning on harvesting that yeast and culturing it to see what I get.