http://www.clayartcenter.com/synair.htmThey're prompt and courteous.
Here's what I purchased from them:
Pour A Mold S333
Pour A Kast Mark15
Synlube 531
Wayne Johnson uses PAK Mark2 I believe. I'm not quite as confident in my own pouring skills so right now I'm using the Mark15 although my next order will probably be Mark3 or maybe Mark2.
Their web page online ordering is kind of messed up so I recommend calling them. Some of the products listed in their PAM page is obsolete and some of the links don't work anyway.