Sourdough starter

Why not capture your own? I did this in Montana .  Find an aspen or birch tree , make a sterile dough ,water flour a little sugar ( enough to capture a sample and enough to feed the starter culture as it grows).   Make this in a zip lock bag   .  Rub the dough on the white bark  seal the bag ,and put it in the oven (off) with the light on. Let it do its thing. It might take a couple of tries but it worked for me. Local fruit with a skin grapes ,plums  any thing using Julia Child's method in Baking with Julia works even better  ,dried up frozen fruit still on the tree will work . I found a old plum half in the fruit dryer worked fine. Don't expect miracles, this takes time and a little luck . Good luck.