If you can find a source of vermiculite from home insulating companies, it should be cheaper than from nurseries. The vermiculite mines that had asbestos in them have been closed for decades.
http://www.dhs.wisconsin.gov/e...
"Vermiculite mined today for use in insulation is from a source considered to be free of asbestos contamination. "
If the "insulation vermiculite" is coarser than you want, just rub it between your palms and you can reduce it to grit, sand or powder very easily. You can screen it with 1/8" tulle or window screening in an embroidery hoop.
However, if you find cubic yards of vermiculite in your attic, don't go rooting around in it or re-use it in the garden. Old enough vermiculite CAN have asbestos mixed in.
