Some years ago vermiculite originating from one particular mine in the United States was found to contain certain levels of asbestos and the mine was shut down.
The vermiculite sold today shouldn't contain asbestos and should be available readily. Nevertheless, it's a good idea not to breath any dust that emerges from handling vermiculite. Once vermiculite is wet, there is no more danger from airborne particles.
Best places to look for are garden centers, pet shops and hydrophonics shops. Vermiculite is also available online from many places.
Please read the following links for more information:
http://www.atsdr.cdc.gov/asbestos/vermiculite_overview.html http://www.epa.gov/ebtpages/airindoorvermiculite.html
