Sacramento, Portland, Boston, Detroit, Minneapolis, London, Washington DC, Philly, Pittsburg? and I am sure many other cities have had Tween Rides/Runs.
FWIW I wear my Tweed jacket on occasion when the weather permits, usually while riding my DL-1 or my Sports, and no I am not on a Tweed Run it is just what I happen to be wearing. If I wanted to do an odd ride for me I would wear lycra.
Aaron