Where can i buy Clay, Plaster and cinder block?

I'm not far from the beginning level in sculpture but I'll be taking AP Studio Art next year so I'm going to start practicing. Where can I buy this materials. I live in Los Angeles. Online stores are good as well. Clay Fine Grogged and Red Terracotta Fine Scrim, Plaster, Cinder Block, wood and wax. A ton of other things. But I don't know what brand or kind. Clay alone has like a whole bunch of different kinds and is frustrating! HELP!!!!!