Airstream's online store now has a short sleeve Argosy T-Shirt and it also references an Argosy hat (though the hat in not available on the website yet).
RickO here on the forums actually got a tan Argosy T-Shirt and hat off of eBay last month - seller was Airstream. The T-Shirt offered on the online store appears to be the same, but is a darker color. I'm sure they will have the hat available on their site real soon too.
Airstream's online store is located at: Airstream :: Store