Try A-Plan Chapel Court Thatcham Berks RG18 4QL 01635 874646 - not all branches will cover it.
I have been with them a few yrs now and always shop around.
Price did increase a lot last time around but I stuck with it.
2010 C6 Lots of mods inc supercharger, runs 650 bhp and 650 torque.
Limited 5k mls paid under £440