Clandestine has moved to Bovey Tracey and Stayer are based in East London as far as I’m aware. You could try getting in touch with Andrew Densham at “one tube at a time” but I think he’s been quiet of late. BTR and Starling are both in your area, so might be worth getting in touch with.
Clandestine Cycles would be a good person to get in touch with. They have a workshop up near the arches in Bristol.