If you do a lot of baking, you are going to want to get yourself a good lively sourdough starter. Here are some options.
Steal one. Is there a bakery in your town that sells uncooked, bake-at-home sourdough bread dough or pizza dough? That’s basically sourdough starter with the addition of other ingredients—hopefully just salt. Take it home, make a mixture of 1/3 bakery dough, 1/3 flour, 1/3 water, then let it cure until bubbly. Throw away 2/3 of the mixture, and repeat with the flour and water. Do this every couple of days for a week or two. Eventually the side ingredients will be minimized and you’ll have some nice starter. (If the dough contains eggs or dairy, which is unlikely, this method won’t work.)
Borrow one. As in the process above, bakers are always throwing away excess starter in the process of refreshing their starters. If you know somebody who bakes sourdough bread, ask if you can have some starter. Unless they’re a jerk they will be happy to share.
Start one. This should be drop dead easy… just mix up some rye flour (which naturally contains more yeast beasties than white flour and more sugar to feed them) and water, allow to sit covered with a cloth or paper towel for a few days until it starts fermenting, then cultivate by repeatedly discarding 2/3 of the mixture, mixing in unbleached bread flour and bottled water (in case your tap water is treated) to refresh, waiting till the new batch becomes bubbly, then repeat. I have had mixed success with this method however… I think that bad beasties from the air sometimes overpower the benign ones in the flour. A clever hack is Pineapple Starter…. The acid in the pineapple juice fights off the bad beasties (including mold) while providing a fertile environment for growing the right kind of yeast.
Once you have a good working sourdough starter, take care of it. Put it in a tight fitting glass jar in the back of the refrigerator and label it so your wife doesn’t throw it out like mine once did. Each time you use the starter you will spoon out the contents of the jar, then replace with a replenished starter made as part of your recipe. You do NOT need to wash the glass jar every time; once in a blue moon is sufficient. Do, however, keep the rim of the jar clean so the lid will easily open and close.