Nurseries, Feed stores, the people that supply the nurseries (Just ask them, they'll tell you).

Thanks for the suggestions!

I drove by some nurseries that were not open yet...I have a few garden supply stores near me that would probably have it, but would also cost a lot.

Now I didn't think of feed stores. We have lots of them around. I will try those next.

I got my course vermiculite at a swimming pool contractor. They use it as "pool base".