Peter Burgess in Alfreton is supposed to be very good. I believe they recently had a state of the art rolling road fitted too.
There is also a rolling road in Ripley just off Nottingham road.
cant remember their name , think it was Dynotech, i spoke to them about setting up my carbs before i sold them, and they seemed very knowledgeable and said getting weber parts was not a problem. Next time i go past will get their name and number for you