https://www.hatsandcaps.co.uk/
Maybe this?
Huh, don't think it was (site I'm remembering was slightly less overwhelming with choice than this one!) - but it looks like a good place to start trying to work out what sort of hat guy I might become....
@owl started
London Fixed Gear and Single-Speed is a community of predominantly fixed gear and single-speed cyclists in and around London, UK.
This site is supported almost exclusively by donations. Please consider donating a small amount regularly.
https://www.hatsandcaps.co.uk/
Maybe this?