I used to get some off the old abandoned rail road track and our old gravel road, before it was black topped. I have a pile of them which I polished. They look very good. Sometimes garden nurseries have them. Check there.
There are some places here and there. A local rock shop can tell you a few good places to look. It's fun to pack a picnic lunch and spend a day someplace, but if all you want are a few pretty rocks it's cheaper to buy them at the rock shop.