http://www.italparts.com/index.html
From a recent Dr etc. thread.
http://www.racetechfab.com/roadracing.html
Russ nyberg fabrication roll cages etc
from a recent roll cage thread.
I think there are some more links that people have been posting elsewhere, I'll scavange for them later, but we gotta encourage everyone to add thier links to this list! It is such a valuable resource.