We live on Dartmouth Road and was refused by every local GP originally as we seemed to border all the catchment areas without actually being within one. It was a few years ago and I remember contacting someone within the NHS who had the power to select and force one of the local GP's to accept us. You might want to try contacting the local PCT as I believe they have powers to enforce placement.
Lewisham PCT
Cantilever House, Eltham Road, London, SE12 8RN
Tel:020 7206 3200
Probably worth a try contacting them! Good luck.