It's US Airways, Mr V., this lady is flying into Charlotte.
Yes, I couldn't get a lot of joy from the website either - found myself here.
http://www.usairways.com/awa/content/traveltoo ls/specialneeds/mobility.aspx
They seem to want to do things via phone - not email.
I've never failed yet to get a US website to accept a UK postcode in the zipcode box - but couldn't find the form that you have.
Have you tried phoning them/ - I doubt that they will dole out email addresses.