There's a 20 group;
http://www.raleigh20.co.nz/
Actually there's lots of 20 stuff on the web. considering that shipping is easier for these, I'd say Ebay would be the way to go. Top dollar would probably be for a well cleaned and polished bike that looked stock. A Brooks looks great on these if you've got one to spare.
I'd have a real hard time not monkeying with it some before I let it go though.