I use this guy, he is brilliant, he is based in Cringleford but will come to you.
http://www.drivecool.co.uk
He has done a couple of mine, he is more than happy for you to supply a new condensor and fit it if it is a stone in it, or he can fit it for you. Whatever works out best for you.
He has replaced a leaking seal on the valve a couple of times and charged me £5 to fit a new seal, and then the regass price. So he doesn't take the piss.