Thanks Joelle, but I am not THE expert. I have only the sensitivity to sulfite. What your husband has sounds like the true allergy, far more serious. A couple of others know this side of sulfite better.
One good reference is http://www.learningtarget.com/nosulfites/index.htm
Rick explains how foods are processed, how to calculate how much is in foods and how much a person tolerates. You can email him to discuss your findings.
I'm interested in knowing what brands of starches you have found to be sulfite-free. They may not be available here. I'll definitely do some searching. Thanks so much for the tip!