Plenty of clapham is free on single yellow on Sunday, there even some bits that free permanently, but they are extremely busy and hard to get.
I suspect you could even get closer then that if some is familiar with areas such as stockwell vauxhall ...etc.
Bikepunx might be able to help I'm sure they laser cut the rings. I have an incredibly strong stainless steel one from them, I'm sure aluminium is do able.
Fibre lyte for the carbon.
May be try spray.bike
Left over cans are available of FB market place to practice with, I've heard good things, when the work is put in sanding between layers. Lots of colours and finishes available.
I'm with you on this one. For cycling to become normalised in London for most people it will need to part of the transport solution not the solution.
Remind you to shout at the next Brompton riders on the tube or buses...unacceptable behaviour.