Just an FYI for anyone in the PDX/Vancouver, WA area who might want to mix up a batch of Al's potting mix, I've just finished recon and made the necessary journey to obtain the main components for the mix. I want to share the locations where they can be obtained so you can have the hours of my life that I frittered away on the web and the phone...
Turface
Hobbs & Hopkins
1712 SE Ankeny St.
Portland, OR
$14.95/50 lb. bag
#2 Grit
Orchards Feed Mill (but most feed stores will carry some version of this product)
6017 NE 109th Avenue
Vancouver, WA
$10.95/50 lb. bag
Fine Fir Bark - (The only stuff I could find was Black Gold 'Fine" Orchid Bark. It's not quite as small as Al's, but it should do. I hear rumor that the Portland Orchid Society offers fine fir bark too, but I haven't been able to reach anyone to confirm this.)
Rain or Shine Garden Supply
13126 Northeast Airport Way
Portland, OR
$4.50/ 8 qt. bag
Gypsum
Shorty's Nursery
10006 Southeast Mill Plain Boulevard
Vancouver, WA
$5.95/5 lb. bag
It took a bit of running around, but if you take my route, you get to visit a couple of great locally owned gardening shops, a wonderful feed store (now I know where I'll be buying bird seed for the rest of my life) and, if you're a Washington resident and enjoy an occasional nip, while you are across the river you can stop at Rose City Liquor and stock up on spirits for about 50% less than we now pay here in WA.