Go to HD or Lowes, in the garden section, 40lb bags are right ~$4.50. Do not order online, the shipping is easily 3x+ what the product cost.
Also, don't ruin your grinder trying to grind rocks. The pellitized lime IS flour, shaped into pellets and held together with a fast dissolving clay binder. The flour is released with the first watering. I have and use both the pelletized and straight flour lime. There is zero difference in results.
The pelletized lime is mainly used in the raised bed gardens and any top dressing. If you've ever tried to spread the flour outside with even a slight breeze, you really come to appreciate the pellets.
Wet