Where can I buy materials used to make a Running/Fastpacking type pack?

You might be interested in this if you’re not already familiar: http://sub60.wikispaces.com/pack

Your interests seem aligned with his.

Rene, thanks for the mention of the sub60 pack. RE the UD "hex mesh": If we're thinking of the same thing, that stuff is pretty cool. I couldn't source it nor does it have big enough holes to work with my design. In the end, I went with a USA sourced 100% nylon utility mesh. I'd be happy to direct you to that source if it looks like what you want.
RE the stretch mesh: check out Quest Outfitters (online). They have two weights of lycra mesh. I've had good results testing this material for a forthcoming update to the sub60.

Thanks for the feedback. The Sub60 looks cool but not exactly what I'm looking for…I want to make something more like a large capacity running vest than a backpack. Thanks for the recommendation on Quest Outfitters, I was wondering if it was worth ordering some of that stuff. I'll probably go ahead and get some and try it out.

Still no word from UD on their hex mesh etc – I received a reply from their customer service saying they would forward me request to the product development team, but that's all I've heard so far. I'm guessing it may be proprietary stuff that they developed and may not want it out there for the general public.

Hi Allen,
I found a fabric that meets your criteria of being lightweight, non stretchy, nonabsorbent and tough.

I had bought a construction safety vest a while ago from a local overstock store with the intention of turning it into a Matt Kirk sub 60 pack following his generously-available instructions, yet I'm still working my way through a long queue of MYOG projects and haven't gotten to it yet. I have worn the vest extensively for running and hiking during hunting season and have no tears or snags to show for it. While it's not branded as Hex Mesh, it looks similar and performs great.

Additionally, these style of vests have a soft, nonabsorbent binding that you could repurpose as well. Maybe try picking one up and seeing if you could repurpose it? I found mine for under $5, but I frequently see them at thrift stores and work wear stores for $2-$20. Only thing is the color selection is limited :) (But maybe you could dye it?)

I'm not sure if the overstock store near me still has them but if you have trouble sourcing it let me know.

Greg, thanks for the tip, that actually sounds like a great idea…my project is on hold for a bit but I'll definitely keep that in mind when I come back to it.