Most of the cutting-edge lightweight gear is produced by small "cottage industry" manufacturers (often only one or two person firms) who sell only on the internet. Very few of their products are sold in retail stores. Most retail stores don't want to carry true lightweight gear because lighter weight gear has to be handled more carefully, so the stores who do unlimited warranties (like REI) only want to carry bomber-proof stuff. "Cottage Industry" gear is also not produced in sufficient quantities for selling at retail. The market is, after all, relatively limited.
I don't know how old this list of "cottage" industries is, or who compiled it (someone on BPL, I know), but this is good for a start:
https://spreadsheets.google.com/pub?key=p1BeDPszxH2no25mC7SLwCA
I suspect that this list is several years old because I don't see some key new firms on it. It also shows the BPL Gear Store as open, which it no longer is. There may be others that no longer exist. IMHO the best way to find new firms is to follow on the BPL forums. New firms will announce in the "Gear Deals" section.
Firms not on this (but should be) that I know about include: Elemental Horizons (packs), Goose Feet (marvelous down booties), Katabatic Gear (quilts and bivys), Hyperlite Mountain Gear (packs, shelters), Bear Paw Wilderness Designs (shelters), Lawson Equipment (lots of misc. items at excellent prices), QiWizUlGear (Rob Kelly's Ti potty trowels, saws, stoves), Ruta Locura (split from Titanium Goat). I'm sure there are others that I've missed.
You mentioned a UL shelter, such as the ZPacks Hexamid. ZPacks only sells direct on the internet. I have one but (due to a foot injury) haven't been able to use it in the field yet and probably won't until fall. So far, though, at least in the back yard, it appears to be exactly what I want! For ultralite shelters (under 20 oz. for a single shelter), John Abela's website has a really good summary: http://hikelighter.com/2011/12/29/sulxul-enclosed-shelter-comparisons/
As mentioned, going to the Bay Area "GGG" gatherings announced on this forum will let you see a bunch of excellent gear never found in stores.