There are several recipes for sourdough starters using potato flakes - oddly enough all of them I looked at also contain commercial yeast...Here's a link to a few I found and you might also try googling "sourdough staters using potato flakes" to see if you can find what you're looking for. Here's the link:

http://www.angelfire.com/ab/bethsbread/sdPotatoFlakeStarter.html

 Good luck and have fun baking!

Trish

here is a link to the one I use.  BTW, I use the recipe itself for most of my sourdough breads, just substituting what ever starter I want to use.  My SO loves the mild SD taste of the potato flake starter bread.

http://www.cooks.com/rec/doc/0,164,148168-242201,00.html

Bob

If you want to get a true sourdough starter -- i.e., a starter that consists of wild yeasts and bacteria -- you just can't go wrong with Sourdolady's method. It works.

As for potato flakes, the yeast and bacteria will certainly love the complex carbohydrates in them. It's not necessary to feed a starter potato flakes, but if you like the flavor it produces, once it's established, go ahead! Carl Griffith, whose starter is given away freely by Carl's Friends, used to feed his starter potato flakes, as you can see here. But again, plain flour works just fine, too.

If you don't want to start one up, you can get one free from Carl's friends, above.