Where to find Silica sands(very fine!!)
I don't know if this will help you find the very fine silicas,but try US Silica(google it);they also show that they have the metakaolins as well.I think you'll have to contact your regional rep(they're listed)or if you're lucky and live in the SE of the US,or Texas,you could probably go to the plants where this product is produced.
Here in Canada,Sil-Co-Sil is the product I get from the Mad Potter in Richmond,BC.Prices will vary from area to area.My bags are from US Silica ;some places may repackage.Some pottery stores(one in Langley,BC comes to mind)does that and puts it into smaller batches.
If you use it,BE CAREFUL.This stuff is bad news for your lungs.I declare here that those who use this and no respirators are nuts!And that language is toned down so as to not offend.Don't play with it unless you're properly prepared.I'll now yield the soapbox to someone else who wants to say that they don't use protection.BTW,this stuff stays in the air for a bit even after CAREFUL handling.
Cheers from here