I just found this thread and am kicking myself that I hadn't posted this little bit of research.
Please use this to get some ideas, for your car. I don't endorse any of these folks (yet), but please comment on any that you have experience with.
Please feel free to post any sources for roll-bars and roll-cages that you know of:
1.
http://www.cachassisworks.com/cages.htm
2.
http://www.chassisengineering.com/rollbars.html
3.
http://www.ioportracing.com/
4.
http://www.cscracing.com/COBRA.htm
5.
http://autoweldchassis.com/rbc.ivnu
All the best,