Anyone know where to find it?
Playground sand boxes, along riverbanks, there are some sand islands if you’re near a lake. Hardware stores out back. Vollyball courts.
Hardware stores (the ones with tons of building supplies on display racks) have canvas sacks of sand for easy transport. They also have other useful stuff in abundance: nails, quicklime, coal, lumber, cement.
You can also find sandbag fortifications rarely on roads near bridges, and yeah wherever else you’d expect to find sandbags.
Edit: Didn’t see that last part of 1st reply, my bad.