From what I have read, fungi is everywhere. I just read a thread about beginning a wild yeast sourdough with the fungi that is on the purchased wheat berries.
I have heard that even though you can start with an obtained source for sourdough starter, eventually, local fungi will take over the starter, that makes sense, to me. The local fungi are best suited to the local conditions.Therefore the local fungi should be able to "take over" the wild yeast sourdough starter that you nurture.
If your starter is gonna end up there, why not start with that??