If you use Apple Mail, you should know about a site called http://www.hawkwings.net/ for “tips and add-ons to make Apple Mail even better”. It’s a great resource, and on it I saw a UK mail icon set back in 2006. From that point onwards knew a computer of mine with an american eagle looking at me would feel wrong. The download wasn’t there however, but I did manage to track down the person who had made it. Having a look again now in 2009 the original site seems to be back up complete with downloads, but back then he emailed me the photoshop file, and I took the template and remade the first class icon afresh into a bold red worthy of nostalgia (first class is gold nowadays, natch) and graphically fitting with its icon peers in the dock.
And so here for all is the icon, and if you want it, the photoshop file.