I second EBAY. I see you're in Canada, Olam, but for sellers in the US check out:
http://stores.ebay.com/CRYSTAL-SEEN
http://stores.ebay.com/Arrowhead-Crystal-Mine
http://stores.ebay.com/CRYSTALMINER-QUALITY-MINERALS
http://stores.ebay.com/Natureskind
I have bought from all these and can recommend. There's hundreds of sellers on EBay, just search.
Also, off EBay quartz, see:
http://www.bluemooncrystals.com/
http://www.arkansasquartzcrystals.com/
http://www.jimcolemancrystals.com/
The last one sells flats. For bulk, try searching "arkansas quartz flats". Good luck.