This may be of interest to anyone else who's been bitten by the GTD virus...
Years ago (some time last century, as a matter of fact), I came across a rave review for something called a Pocket Briefcase -- a little leather case for holding index cards suitable for taking notes and organizing small bits of paper. It makes a good foundation for analog PDA, and it's slightly more versatile than a $1.00 memo pad from the local drug store. That review made such an impression that I broke down and bought one the first time I saw it in a store a year or two ago.
These cases work well with any 3"x5" index card, but generally work best with unruled, grid ruled or portrait ruled index cards. Regular index cards are ruled the wrong way, since it's most comfortable to hold the case in a "portrait" orientation. (Levenger sells a whole assortment of overpriced 3x5 cards with the proper orientation, for use with their pocket briefcases).
In the mean time, I've been buying pads of portrait-ruled index cards. The local office superstore always has a ready supply of them, $1.29 per 100. So they're cheap and they're easy enough to find.
Except online. I was trying to point to these products in a mail message, and none of the regular stores seem to sell them online.
Today, I stumbled across the magic incantation to find these products on the web. Outpost.com sells them over the web in both white and violet.