You can easily start your own and have it ready in just a couple weeks to bake with. Basically just add equal parts flour and water and mix together. Wild yeast naturally lives on the flour (or in the air) and will colonize. Then the next day, just take a bit of the previous day's starter, combine with more equal parts flour and water. Do that every day and after a week to 10 days or so, the wild yeast will be firmly established. Your stater will start smelling yeasty, slightly sweet and fruity, and a little vinegary (at least mine does). About 8 to 12 hours after you feed it, it will bubble up and double in size, which is when you want to use it in baking. After it is established, you can store it in the fridge and only have to feed it once a week or when you use it.