I figured I would start a thread for what its worth, of a few links i found, feel free to add more links.

Some grilles and accessories
http://www.premiermotoring.net/cgi-bin/webc.cgi/trailblazer.html

Only body kit I have found
http://www.sporttruckdirect.com/SSE_02_TrailBlazer_Envoy_Body_Kits.html

Wheels
www.superbuytire.com
www.wheelmax.com

Audio
www.ebay.com (the best and cheapest)
www.crutchfield.com for info as to what size speakers you need, item numbers to look up on ebay, install kits, wiring, etc, but this place is super expensive
www.sounddomain.com

General Info
http://www.new-cars.com/2003/chevrolet/chevy-trailblazer-specs.html

Lug pattern is 6x5''

Feel free to add anything else!

Josh