Hi Dave, Glad to have contributed an idea for your website. Here is a few used brass dealers to find used brass instruments:

Dillonmusic.com
Brassark.com
Wichitaband.com
Robbstewart.com
Oberloh.com

Hopefully others reading this post will add to the list. One thing about used dealers is that they probably have checked out the instrument with some level of expertise, but in the end "Buyer Beware"