Research wild yeast. Yeast spores are actually floaring around your head right now-they are dispered naturally in the air. You can start your own "starter" with flour water and sugar. Warmth helps the naturally occurring yeast to develop and grow.

This from: [link to joejaworski.com]

To capture wild yeast, place one cup of bread flour and one cup of water in a glass jar. Cover the jar with a fine mesh (a knee-hi stocking works well) to let air in but keep bugs out. Place the jar outside where it can receive some fresh air and some breezes. Best location is a shady spot. Let it set for three or four days. Stir one or twice a day. If it is cool outside ( 35F(2C) to 60F(16C) ) you will see very little or very low activity in your starter until you bring it indoors and warm it up. If it is less than 35 deg F, wait until warmer weather before trying to capture yeast. If the starter turns pink or dark grey in color, it has become moldy and you should discard it.



If you see no bubbles in the mixture after a few days, discard it and try again. If you see lots of bubbles in the surface of the mixture, congratulations! Feed the yeast with another cup of flour / water mixture and let it ferment indoors for another 12 hours or so. After that, try an experimental loaf. Even though you may not live in a place famous for sourdough, you will be surprised how tasty native yeast can be.