I'm on the Big Island and my local hardware store only has normal poultry grit. I had no trouble ordering chick grit from Amazon and having it shipped to Hawaii, though. This is the specific one I ordered: https://www.amazon.com/dp/B01N7KBFCS/?tag=backy-20
Chick grit is about the same size as chick crumbles. You can definitely substitute coarse sand or other similar size rocks from the ground. Do wash the sand first.
ETA: rougher shapes are better than smooth.