I am in Mississippi.
I don't think they believe in hardware stores....everything here is built with duct tape and bailing wire.
I will check the local Lowes though.
Scott's right: much of it can be found in the plumbing section at Lowe's / Home Despot / Ace / Tru Value / whatever.
A manifold, for instance, can be made from a tee or a cross... 3/8" seems to work well, though 1/4" is okay. I don't find a lot of fittings use 1/2" (and these are all NPT thread sizes, btw!) My distribution manifold under my hood is a coupla maybe 2" long pipe nipples with a bunch of tee's between. Seal it up with some thread goop, works nicely and is easy to mount with strap to whatever.
Filters are a bit trickier; I got mine from Sears on a closeout (they don't usually stock them in the stores any more), but all you need is something with pipe thread (actually, for this I did use 1/2", figuring to get as much air into the compressor as possible) and some cardboard in it =)) Some places will carry them in their lawnmower parts -- look for someplace that services lawnmowers or air compressors, or worst case, ping me and I can dig you up the Sears part # to order from them online.
The pressure switch, however, I was *totally* unable to find locally and had to get from Kilby. (I mean, you could order from McMaster or Grainger, prolly, but they're all gonna ream you, grrr.)
HTH.
-- A