I came across one in a market town charity shop just before last Christmas. A bit like a vintage Madras jacket in overall appearance, half sleeves, label that suggests shtick, but at four quid for a summer shirt seemed not unreasonable. Looks okay with jeans and desert boots. No information as far as I can tell - Ebay yields one other. They seem inexpensive - which is fine by me. Do any of the American posters know anything?
Oh yes, they have a stupid tag on the breast pocket that you have to remove.