Sulphites (or sulfites as they are known in most other countries) are different from other allergens as they are inorganic salts with preservative properties rather than food proteins.
This is not usually a classic IgE allergy as the symptoms are usually either from contact in the form of rashes or exacerbating asthma symptoms, so are classed as a sensitivity or intolerance.
I have put together some more comprehensive resources at http://www.allergyresources.co.uk/Sulphite.php
The allergy resources page for sulphite covers the key allergens, which allergic syndromes sulphite allergy is linked to and other foods which are commonly cross reactive with sulphite.
There is also regularly updated links to useful websites specifically for sulphite allergies and the latest research papers on the topic.
If you have multiple allergies and are interested in how they are linked or want to find out more about food allergies outside the usual top 14 then you can follow me on Facebook or Twitter, where I share a food allergy card every day of the week.