In June of this year I sent a Purdey to the gunsmith at Griffin & Howe so the sidelocks could get strip cleaned and was very pleased with their work and turn-around time. While what I had done is relatively simple compared to what you may need, here's what they say they can do on their website:
Parts and Spring Making:
The Gunsmithing Shop at Griffin & Howe has the capability to create virtually any component contained in the majority of firearms spanning multiple centuries. The oldest firearm they have fabricated a part for was a 1600s era shotgun!
It might not hurt
to check with G&H. 
