For MT and Norther WY suggest Archie Bray Clay out of Helena. Really nice selection of pottery clays. And they have 3 brands of fire clay too. Really neat toy store for anyone into clay or pottery.
Since they are forever changing page links putting the general web address in here first
Archie Bray Clay as that much is as least always stable.
The current link to the materials page is
Raw materials Likely it will only be good for 6 months or a year though so don't be surprised if it dies soon and you have to start from the main webpage and branch down to the page.
Country oriented nerd with primary interests in alternate energy in particular solar. Dabble in gardening, trees, cob, soil building and a host of others.