Two things: coach tickets and feeder rides for the Dunwich Dynamo...
(1) Coach tickets
In 2012 we brought over 800 back from Dunwich on coaches. When I say "we", that's Bermondsey Bill in charge of logistics, and a number of Southwark Cyclists people issuing tickets in London Fields, and Dog & Bell Crew, Francis Sedgemore included, counting heads and bikes on the day. In 2013 we upped the number to 1,000, and had a stash of tickets as a contingency.
I'm afraid that I cannot answer specific questions about ticket sales, as I'm blissfully ignorant about that (and much else besides).
(2) Feeder rides
There are a number of feeder rides to London Fields. In 2012, Francis Sedgemore led a ride from Cutty Sark Gardens in Greenwich, up along the Regent's Canal. In 2012 he went via Southwark Needle, and there collected the Southwark crowd. In 2013 he wanted to avoid the nastiness of rush-hour central London, hence the canal-side pootle. He recommended that southeast London riders coming from points west of Greenwich should make their way along the Thames Path (NCR4) to Cutty Sark Gardens. He thought there might even be an organised sub-feeder ride from Southwark Needle to Greenwich.
See here for details of the Greenwich Feeder...
I see that fellow Dog & Bell Crew member saoirse organised a feeder from Lewisham, but I don't have a web link for this. All I know is that Jane's ride started at Ladywell Fields, and crossed Tower Bridge.