To those saying you can't get certain things, please look at the seattlefabrics.com webpage, you can get all manner of multi-ply gortex brand fabrics, urethane coated fabrics like cordura, silnylon coated nylon fabrics, etc. Just about anything you'll find on a messenger bag or a technical backpacking pack can be found there.

They also sell metal cam buckles meant for 2" dive strap webbing. Those cams are beefy as all hell. You can also get 2" 'seatbelt' style webbing at REI cut to length for a reasonable price.

ITW Nexus also has a 2" secureloc ladderlock buckle that would be strong enough for most messenger bag applications, and would be very simple to use, even as a temporary solution until you track down the 'perfect' hardware.

For the laptop sleeve, you may need to be a bit creative. You can get foam from most fabric stores, and you can get cloroplast from most yard signs (its that white plastic that looks like corrugated cardboard that political yard signs and stuff are made from). If you took a few rectangles and sewed them together on three sides, and then used these rectangles to make a laptop shaped bag, then you could slide a piece of cloroplast with a piece of thin foam glued to it down into the side panels, stitch it closed, and have a pretty handy laptop sleeve. Cloroplast is as good as gold for people make their own gear, since its lightweight, cheap (or free around election time), and easy to work with.

peace,
sam