As simple as it may be, do not do it. I mean, I guess you can. I came off kind of intense there. Truth be told it is a waste of money that will cancel itself out. How? Read on…
Do you know why San Francisco Sourdough is so special? The yeast in the Bay Area are a distinct species of yeast. It is not that the early bakers in the west possessed a particular and special ingredient. The yeast and the specific bacteria they release is the overwhelming factor in sourdough taste.
Many places will sell SF sourdough. It’s not that expensive but it is a waste. You see yeast are everywhere all the time. Say you live in Boston and buy a few cups of SF starter. When you open the container and start feeding it you will be introducing yeast from your environment. Eventually they will crowd out the SF yeast. It is not that they will fight but the SF yeast are finite whereas the Boston yeast are infinite, you do the math.
Just make your own!