Local Grass fed butter?
I don't think I've seen any at a farmer's market. I use Farmhouse Delivery and they offer Lucky Layla's butter $7.50/11.4 oz. Lucky Layla's says that it's pasture fed.
I get my Kerrygold at Costco - three 8 oz bricks per box. They have the individual bricks in the cheese section at my HEB.
One of the dairy farmers at the Barton Creek Farmer's Market used to make a very small amount of butter. I tried it once, but it had turned rancid and was inedible. I've asked Mill King and Full Quiver if they will make either buttermilk or butter and neither one was interested.
Before you despair, you might check with Dyer Mercantile in Georgetown. They sell raw milk, freshly made butter, and superb eggs, chickens, beef, pork and lamb. (I have no business affiliation with them; I just buy their meats and milk.)