I'm here representing Wheelers Off-Road. http://www.wheelersoffroad.com Though we don't have a page on the site Directly for the TrailBlazer/Envoy yet, we are working on a few suspension components for this rig. We can also get the popular BDS kits, along with many other items such as On-Board Air, CO2 systems, Pro-Comp Wheels, Air-Lift Bags, Timbren Suspension Enhancement and much much more.. Let me know if there is anything you guys need.
Thanks

Johnny@wheelersoffroad.com
Here's a quick list of just a few of the companies I can get. Most of our product and supply is specialty high performance, so I won't be able to beat every Ebay and Craiglist price out there. But if you let me know what your looking for I'll do my best.
ARB
Alcan (custom Springs)
BrightBox
BDS Suspension
Betts (custom springs)
Bilstein
Centric (brakes)
Coast Cutlery (Awsome Flashlights)
Cramer-Decker (source CO2 kits)
Daystar (poly products)
Deaver (custom springs)
Deist Safety (seat belt,limit straps ect.)
Excalibur (wheel accessories)
Fox
Gorilla (wheel Accessories)
Goodrige (custom SS lines)
Innova Design
King
Porterfield (brakes)
Powerstop (brakes)
Power-Tank (CO2 systems)
Pro-Comp (enough said)
Rampage Products
RCD Suspension
Rubicon Express
Rough Country
Spider-Trax
Techna Fit (custom SS lines)
Timbren (load carrying bumpstops)
Trail-head (deflators)
Viair (on board air)
Wagan