There are many labs that now do IgG food allergy testing. This isn't quite mainstream, but it appears to be gaining momentum. Here is a link that lists a bunch of labs, and many of them have very good websites which explain the difference between IgE and IgG food allergy and symptoms. There are also a couple of articles about IgG food allergy, too.
This one gives a quick explanation, but check out some of the other sites, too:
This all does get confusing. The difference between celiac disease (biopsy evidence of intestinal damage), gluten sensitivity (positive antigliadin antibody), and other IgG food sensitivity. They can all cause GI and many other symptoms... often of the more 'chronic illness' variety.