I've been racking my brains to remember - it doesn't take long
I'm going to point the finger at ebay. I'm always going to see what bike bits I can pick up and there are always some there, of course. I think I must have seen them there first.
The curious thing, thinking about it, is how FEW I've seen around London on my conventional bike travels. I can only remember one. Pretty amazing.
I saw more (well, it wouldn't be difficult) in my one week in Aldeburgh recently than years in London.