I don't know anything down in SD unfortunately. However, I am fortunate enough to spend a lot of time in Central Coast and have been buying all my meat locally for about a year now. I can't say enough good things about all the people we shop with. Most of which you would need to come up to Templeton or Paso Robles to get.
However, Old Creek sells online and they are a very nice family with wonderful product. They hit many of the farmers markets in the area and recently added really nice pork to their sales (fed often with some leftover avocados also from the ranch). It would really be worth doing a nice big order from them to check it out. And by all means come up to the coast to check them and the others out. If I hear of anything closer, I will let you know.
BTW: Niman ranch is a pretty huge factory operation. It is nothing at all like the small family farm you get with ones like Old Creek.